A wearable air purifier

Abstract

A wearable air purifier compressing headgear 102, a fan assembly 103, 104 operable to generate filtered airflow, and a nozzle 105 releasably attachable to the headgear or the fan assembly, for receivi

Description

Background of the Disclosure Exposure to air pollution such as pollutant gases or airborne particulates presents a risk of harm to human health. An approach to reducing a person’s exposure to air pollution is to use a wearable air purifier to discharge filtered air towards a wearer’s face. 20 25 Summary of the Disclosure A first aspect of the present disclosure provides a wearable air purifier. The wearable air purifier may comprise headgear for wearing on a wearer’s head. The wearable air purifier may comprise a fan assembly operable to generate filtered airflow. The wearable air purifier may comprise a nozzle. The nozzle may be a face contacting or a non-contacting nozzle. The nozzle may be for receiving the filtered airflow generated by the fan assembly, and for discharging the filtered airflow towards the wearer’s face, such as the wearer’s nose and / or mouth. The nozzle may be releasably attachable to the headgear or the fan assembly. The wearable air purifier may comprise an alert system for generating an alert signal for use in prompting the wearer to attach the nozzle directly or indirectly to the headgear. The alert system may comprise a nozzle sensor. The nozzle sensor may sense if the nozzle is attached to or detached from the headgear or the fan assembly. The alert system may comprise an environmental condition sensor for sensing an environmental condition. The alert system may comprise an alert signal generator for generating the alert signal on the basis of the environmental condition sensor sensing the environmental condition meets a criterion (for example, a threshold, such as a predefined threshold), and the nozzle sensor indicating the nozzle is unattached to the headgear or the fan assembly. Providing the wearable air purifier with the alert system reduces a risk of exposure of the wearer to unfavourable environmental conditions to safeguard the wearer. Limiting use of the nozzle to applications when the nozzle is most beneficial helps increase a lifetime of the nozzle and provides flexibility to the wearer. Informing the wearer of specific conditions in which to use the nozzle improves the user experience and enhances an interconnection between the wearer and the wearable air purifier. Wearable air purifiers that detect undesirable air and inform a user to wear a nozzle to enhance a quality of the air to be breathed help in managing the health of the wearer by limiting exposure to the undesirable air. Sometimes, the user may have the nozzle 5 directly or indirectly (e.g. via the fan assembly) unattached, for example, when the user is in conversation with someone, or the wearer requires access to their own face. On occasions, the user may forget the nozzle is unattached. Therefore, informing the user that wearing the nozzle would be beneficial to their respiratory health, in such instances where the nozzle is not worn, enhances the benefit provided by the wearable air purifier. 10 The alert system may be configured to sense an environmental condition using the environmental condition sensor, determine whether the sensed environmental condition 15 meets the criterion, sense if the nozzle is attached to the headgear or fan assembly using the nozzle sensor, and generate an alert signal if the sensed environmental condition meets the criterion and the nozzle is not sensed to be attached to the headgear or fan assembly. The nozzle functions to direct airflow from the fan assembly towards the wearer’s face, for example, closer to the nose / mouth region of the wearer’s face. Thus, the fan 20 assembly may be attached to the headgear at a location relatively remote from the wearer’s face, for example, at the side, top, or rear of the wearer’s head, thereby avoiding obstructing the wearer’s face, for example, obstructing the wearer’s vision. Whereas, notwithstanding that the fan assembly may be relatively remote from the wearer’s face, the filtered airflow may still be provided relatively directly to the 25 wearer’s nose and / or mouth via the nozzle, thereby reducing dilution of the filtered airflow by unfiltered ambient air prior to inhalation. The nozzle may, for example, be arranged to extend from the fan assembly in front of the wearer’s face, to thereby duct airflow from the fan assembly to the front of the wearer’s face, for example, to the wearer’s lower nasal and mouth region. 10 15 20 25 The nozzle is releasably attachable to the fan assembly such that the nozzle may be reversibly attached and detached by the wearer. Thus, the wearer may attach the nozzle when the provision of filtered airflow by the fan assembly is desired, and detach the fan assembly from the headgear when the airflow is not desired. The headgear may thus be used without the nozzle attached, and thus without the additional mass and bulk of the nozzle. This may be useful where the headgear has functionality independent of the provision of filtered airflow, for example, where the headgear comprises a headband, hat, helmet or headphones. In such applications, the wearer may desire to wear the headgear, for example, the headphones, without the nozzle in scenarios where the filtered airflow is not desired, such as in environments with low levels of air pollution. In environments with high levels of air pollution, the wearer may desire to also receive the filtered airflow to reduce their exposure to the air pollution. The headgear and components thereof may thus have dual functionality, which may desirably reduce a perceived need for the wearer to have separate air purifying and non-air purifying headgears, for example, separate air purifying and non-air purifying headphones. The fan assembly may comprise a port configured for attachment of the nozzle to direct the filtered airflow to the wearer of the wearable air purifier. The headgear may comprise the nozzle sensor. The fan assembly may comprise the nozzle sensor. The nozzle sensor may be configured to detect attachment of the nozzle to the port and to transmit a detection signal upon detection of attachment of the nozzle. The wearable air purifier may comprise a memory. The memory may be configured to store information associated with the nozzle. The wearable air purifier may comprise a fan controller. The fan controller may be for controlling operation of the fan assembly. The fan controller may be configured to: receive the detection signal; analyse, based on the detection signal, fan speed settings associated with the nozzle from the information stored in the memory; and operate the fan assembly using the at least one fan speed setting selected from the information stored in the memory. 30 When the wearer has detached the nozzle from the fan assembly, for example, when the wearer is using the apparatus for a function other than provision of filtered airflow, the wearer risks being subjected to unfiltered ambient air, which may be injurious in highly polluted areas. This risk is reduced by the apparatus sensing an environmental condition and subsequently generating an alert signal if the sensed environmental condition meets, for example, matches or surpasses (for example, exceeds), the criterion 5 and the nozzle is not currently attached to headgear or the fan assembly. Thus, in a scenario where the wearer is wearing the headgear without the nozzle attached to headgear or the fan assembly, but the environmental condition is determined to meet the criterion, the wearer can be alerted to the environmental condition by the alert signal to thereby prompt the wearer to attach the nozzle, to thereby receive filtered airflow from 10 the fan assembly to counter the adverse environmental condition. LD 20 The environmental condition may be indicative of air quality in an environment surrounding the wearable air purifier. The environmental condition sensed may, for example, be one or more pollutant gases in the ambient air, such as, nitrogen dioxide and / or another pollutant gas in ambient air, and / or particulate matter, such as PM2.5 sized particulates. In these examples, the criterion, may be a concentration of the sensed gas or particulate pollutant, such that pollutant concentrations meeting a threshold concentration, for example, pollutant concentrations equal to or greater than the threshold concentration, result in generation of the alert signal. The environmental condition may be indicative of a concentration of particulate matter, such as PM2.5 sized particles, in an environment surrounding the wearable air purifier. The wearable air purifier, for example, the headgear, may comprise an alert indicator, wherein the alert system is configured to communicate the alert signal to the alert 25 indicator. On receipt of the alert signal, the alert indicator may indicate an alert to the wearer. The alert indicator may be configured to generate feedback to the wearer. For example, the alert indicator may be configured to indicate by generating audible, haptic or visual feedback to the wearer. For example, the wearable air purifier may comprise a device for converting the alert signal into a wearer-perceptible alert, such as a visible, 30 audible or haptic alert. An example of a visible alert is a notification that is displayed to the wearer. An intensity and / or frequency of the wearer-perceptible alert may increase over time. The wearable air purifier may be configured such that the wearer-perceptible alert can be deactivated by input from the wearer or after a predetermined amount of time, such as 20 seconds. The alert signal may time out such that the wearer-perceptible alert is inhibited, for example, halts temporarily or stops entirely. The alert signal may 5 cause an additional wearer-perceptible alert that is of the same type or different in type to the first wearer-perceptible alert. The wearable air purifier may comprise an illumination device for emitting light in the visible light spectrum, and the wearer-perceptible alert may comprise activation of the 10 illumination device. The illumination device may be located on a surface of the wearable air purifier that is visible to the wearer. The illumination device may be controlled to illuminate in response to the alert signal. The wearable air purifier may comprise a speaker system supported by the headgear. 15 The alert indicator may comprise the speaker system. The speaker system may comprise a speaker. The speaker may be attached to the headgear for placement over the wearer’s ear. The speaker system may comprise a plurality of speakers. The wearable air purifier may comprise a right ear cup and a left ear cup, for example each being closed ear cups. Each ear cup may comprise a speaker associated with the 20 respective ear of the wearer. The alert system may be in communication with the speaker system. The alert system may be configured to communicate the alert signal to the speaker system, such as the speaker, wherein the alert signal may be transmitted as audible feedback to the wearer. 25 The wearable air purifier may be communicable with a remote device, optionally being external to the wearable air purifier. The wearable air purifier may comprise a communication device, such as a radio transmitter, for communicating the alert signal to the remote device, such as a mobile telephone, whereby the remote device may generate the wearer-perceptible alert. The radio communication device may be configured to 30 output a radio signal in response to generation of the alert signal. The radio signal may be receivable by the remote device. The remote device may be a personal device, such as an electronic device, for example, a mobile telephone, a smart phone, or a tablet device. The remote device may be wearable such that the remote device may be worn by the wearer. An example of a wearable remote device is a smartwatch. 5 The memory of the wearable air purifier and / or a memory of the remote device may be configured to store historical information about the alert signal and future alert signals. The alert system may comprise a transmitter for transmitting the alert signal to the remote device, remote from the wearable air purifier, in response to the generation of 10 the alert signal. The remote device may comprise a receiver for receiving the alert signal. The remote device may comprise a device for converting the alert signal into a wearer-perceptible alert. Examples of the wearer-perceptible alert provided by the wearable air purifier above apply to the remote device. For example, the remote device LO may display a notification to the wearer that is pushed to the remote device by the 15 wearable air purifier. The remote device may be a wearable device, such as a smartwatch or may be a computing device such as a mobile phone, for example a smartphone, or tablet. CM The alert system may use an onboard speaker to generate an audible alert to the wearer 20 when the environmental condition criterion, such as a threshold, is met, and the nozzle is not attached to the headgear or the fan assembly. An audible alert may be useful for the head-worn format, compared to a visible alert, which may be suboptimal, because the wearable air purifier may be outside of the wearer’s personal field of view. 25 The alert system may be configured to further sense if the nozzle is coupled to the fan assembly using the nozzle sensor following generation of the alert in result of the determining that the sensed environmental condition meets the criterion, such as a threshold, and the nozzle is not sensed to be attached to the headgear or the fan assembly. In other words, after the initial process of determining that the sensed 30 environmental condition meets the criterion, such as a threshold, and that the nozzle is not attached, and the generation of the alert signal, the alert system is configured to repeat the step of sensing whether the nozzle is now attached. Thus, the alert system may determine whether the wearer has attached the nozzle in response to the alert signal. 5 The alert system may be configured to generate a further alert signal if the nozzle remains unattached to the headgear or the fan assembly, for example when the nozzle is not sensed by the further sensing to be attached to the headgear or the fan assembly. In other words, if it is determined by the step of further sensing that the nozzle is still not attached, the alert system may be further configured to generate a second alert to remind 10 the wearer. Thus, the wearer may be further prompted to attach the nozzle. The fan assembly may be fixedly attached to the headgear. In other words, the fan 15 assembly is integral to the headgear and is not releasably attachable in normal use by the wearer. The fan assembly may be releasably attachable to the headgear. In other words, the fan assembly is reversibly attachable and detachable by the wearer from the headgear. In particular, because the nozzle attaches to the fan assembly, the fan assembly and the nozzle may be attached to and detached from the headgear as an assembly, which may 20 allow convenient attachment and detachment of the fan assembly and nozzle with respect to the headgear. The nozzle may be fixedly attached to the fan assembly. In other words, the nozzle is integral to the fan assembly and is not releasably attachable in normal use by the wearer. 25 The headgear may comprise the fan assembly. One ear cup may comprise one fan assembly. The right ear cup may comprise a right fan assembly. The left ear cup may comprise a left fan assembly. The ear cup may comprise the nozzle sensor. The assembly may be integral to the headgear such that the fan assembly is unattachable 30 from the headgear. The wearable air purifier may comprise a fan assembly sensor. The alert signal may be generated on the basis of the environmental condition sensor sensing the environmental condition meets the criterion, the nozzle sensor indicating the nozzle is unattached to the fan assembly, and the fan assembly sensor indicating the fan assembly is unattached to 5 the headgear. The fan assembly sensor may be for sensing attachment of the fan assembly to the headgear. The fan assembly sensor may be for sensing that the fan assembly is attached and / or that the fan assembly is unattached to the headgear. LD The fan assembly may be in communication with the alert system, such that, following generation of the alert signal, the fan controller is configured to cause the fan assembly to generate the filtered airflow on the basis of the nozzle sensor indicating the nozzle is attached to the headgear or the fan assembly. The fan controller may be configured to generate a fan signal if the sensed environmental condition meets the criterion and the nozzle is sensed to be attached to the headgear or the fan assembly such that the filtered airflow can flow from the fan assembly through the nozzle and towards the wearer’s face. The wearable air purifier may comprise a battery to power the fan assembly, for example when attached to the headgear. The wearable air purifier may comprise a 20 conductor assembly to conduct electrical power from the battery to the fan assembly. The battery may be mounted to the headgear. The conductor assembly may comprise a releasable conductive coupler to facilitate releasable conductive coupling of the fan assembly to the battery. The battery may power the alert system. 25 The alert system may be mounted to the headgear. The headgear may comprise the alert signal generator. The headgear may comprise the environmental condition sensor. The nozzle sensor may be for sensing attachment of the nozzle. For example, the nozzle sensor may sense when the nozzle is attached to the headgear or the fan 30 assembly and, upon attachment of the nozzle to the fan assembly as sensed by the nozzle sensor, the alert signal may be deactivated. The nozzle sensor may be for sensing that the nozzle is attached and / or that the nozzle is unattached. The alert system may comprise a detectable member. The nozzle sensor may be or may 5 comprise an optical sensor. The nozzle sensor is or comprises a proximity sensor for sensing a presence of the detectable member that is indicative of the nozzle being attached to the headgear or the fan assembly. The detectable member may comprise a magnet, such as a permanent magnet or a magnetisable magnet. The proximity sensor may comprise a Hall effect sensor. 10 A second aspect of the present disclosure provides a personal air purification system. The personal air purification system may comprise a wearable air purifier. The wearable air purifier may comprise a headgear for wearing on a wearer’s head. The wearable air purifier may comprise a fan assembly operable to generate filtered airflow. 15 The wearable air purifier may comprise a nozzle for receiving the filtered airflow generated by the fan assembly, and for discharging the filtered airflow towards the wearer’s face, such as the wearer’s nose and / or mouth. The nozzle may be releasably attachable to the headgear or the fan assembly. The personal air purification system may comprise an alert system for generating an alert signal for use in prompting the 20 wearer to attach the nozzle directly or indirectly to the headgear. The alert system may comprise a nozzle sensor. The nozzle sensor may sense if the nozzle is attached to or detached from the headgear or the fan assembly. The alert system may comprise an environmental condition sensor for sensing an environmental condition. The alert system may comprise an alert signal generator for generating the alert signal on the 25 basis of the environmental condition sensor sensing the environmental condition meets a criterion, such as a threshold, and the nozzle sensor indicating the nozzle is unattached to the headgear or the fan assembly. The personal air purification system may comprise a remote device communicable with 30 the wearable air purifier. The wearable air purifier and the remote device may comprise at least one of a transmitter and receiver for transferring information such as the alert signal between the wearable air purifier and the remote device. The personal air purification system may comprise an alert signal indicator configured to generate feedback, such as audible, haptic or visual feedback, to the wearer, on the basis of the generated alert signal. The wearable air purifier and / or the remote device may comprise 5 the environmental condition sensor. The wearable air purifier and / or the remote device may comprise the alert signal indicator. The remote device may be a wearable device, such as a smartwatch or may be a computing device such as a mobile phone, for example a smartphone, or tablet. LD A third aspect of the present disclosure provides a method of prompting a wearer. The method may comprise prompting a wearer of a wearable air purifier to attach a nozzle to a headgear or a fan assembly such that the fan assembly can generate filtered airflow and the nozzle can discharge the filter airflow towards the wearer’s face, such as the wearer’s nose and / or mouth. It may be that, when the nozzle is unattached to the headgear or the fan assembly and an environmental condition meets a criterion, such as a threshold, the method comprises generating an alert signal to prompt the wearer to attach the nozzle. The alert signal may be generated on the basis a nozzle sensor indicating the nozzle is unattached to the headgear or the fan assembly. 20 The method may comprise activating the fan assembly when the nozzle is attached to the headgear or the fan assembly to generate filtered airflow and discharge the filtered airflow from the nozzle towards the wearer’s face. The fan assembly may be releasably attachable to a headgear of the wearable air 25 purifier, such that the generating the alert signal may comprise generating the alert signal to prompt the wearer to attach the nozzle to the fan assembly and the fan assembly to the headgear. The method may comprise generating an alert indicator (such as a wearer-perceptible 30 alert), on the basis of the alert signal, to the wearer with increasing intensity until the alert signal is deactivated, for example by the wearer or once a predetermined amount of time has elapsed. Any feature or features of any one of the first to third aspects may be incorporated in 5 any other of the first to third aspects. For example, a feature or features of the wearable air purifier of any one of the first to third aspects may be incorporated by the wearable air purifier of any other of the first to third aspects. Brief Description of the Drawings 10 In order that the present disclosure may be more readily understood, embodiments of the disclosure will now be described, by way of example, with reference to the accompanying drawings, in which: 15 Figure 1 is a schematic perspective view of a wearable air purifier embodying the present disclosure; Figure 2 is a schematic front elevation view of the wearable purifier; Figure 3 is a schematic partially exploded perspective view of the wearable air purifier; 20 Figure 4 is a schematic partially exploded front elevation view of the wearable air purifier as part of a personal air purification system; Figure 5 is a schematic front cross-sectional view of the wearable air purifier, Figure 6 is a schematic partially exploded front cross-sectional view of the wearable air purifier; Figure 7 is a schematic side elevation view of the wearable air purifier; Figure 8 is a further schematic side elevation view of the wearable air purifier; Figure 9 is a schematic depiction of an alert system of the wearable air purifier; Figure 10 is a flow diagram depicting an example alert generation process performed by 5 the alert system. Detailed Description of the Disclosure A wearable air purifier 101, embodying aspects of the present disclosure, is shown schematically in Figures 1 and 2. As will be described in further detail herein, the 10 wearable air purifier 101 is configured to be worn on a wearer’s head and deliver a filtered airflow towards a lower nasal and mouth region of a wearer’s face. Consequently, the wearer’s exposure to ambient air pollution may desirably be reduced. 15 The wearable air purifier 101 comprises headgear 102 for mounting on a wearer’s head, a pair of fan assemblies (left fan assembly 103 and right fan assembly 104), for generating filtered airflows, and a nozzle 105 (or ‘visor’) for directing the airflows from the fan assemblies 103, 104 towards the lower nasal and mouth region of the wearer’s face. The nozzle 105, which in this example is a non-contact visor, provides a structure for directing the filtered airflows from the wearable air purifier 101 to the wearer. 20 The headgear 102 has the form of over-the-ear headphones, and comprises a headband 106 and left and right ear cups 107, 108 connected to respective ends of the headband 106. The headband 106 is arcuate, and is configured to overlie a top and sides of the wearer’s head in use, to thereby support the ear cups 107, 108 over the wearer’s left and 25 right ears respectively. The headband 106 is formed to resiliently hold the ear cups 107, 108 against opposite sides, i.e., left and right sides respectively, of the wearer’s head, to thereby firmly retain the headgear 102 mounted on the wearer’s head. The headband 106 is resiliently flexible to accommodate differing distances between the ear cups 107, 108, and so differing wearer head widths. The ear cups 107, 108 are pivotally mounted 30 to the respective ends of headband 106, to facilitate pivoting of the ear cups 107, 108 to accommodate different wearer head shapes. The left and right ear cups 107, 108 comprise respective speaker housings for housing components, such as respective speakers, as will be described in further detail with particular reference to Figures 5 and 6 (see speaker housing 504 and speaker 505, for 5 example). The speakers in the ear cups 107, 108 may thus be supported by the headgear 102 over the wearer’s ears, e.g., to facilitate use of the headgear 102 as headphones. The ear cups 107, 108 comprise respective annular cushions 109, 110 for cushioning against the wearer’s head. 10 The fan assemblies 103, 104 are releasably attachable to a respective one of the ear cups 107, 108, such that the headgear 102 may releasably support the fan assemblies 103, 104 at left and right sides respectively of the wearer’s head. The nozzle 105 is also releasably attachable to the fan assemblies 103, 104, such that the fan assemblies 103, LO 104 releasably support the nozzle 105 at left and right sides of the wearer’s head. The 15 releasable attachment of the fan assemblies 103, 104 to the ear cups 107, 108, and the releasable attachment of the nozzle 105 to the fan assemblies 103,104 will be described in further detail with reference to later Figures. CM The nozzle 105 is attachable at left and right ends 111, 112 to a respective one of the fan 20 assemblies 103, 104 of the headgear 102. The nozzle 105 defines air inlets at the left and right ends 111, 112, to mate with respective air outlets of the fan assemblies 103, 104, to thereby receive filtered airflow from the fan assemblies 103, 104 when so attached. The nozzle 105 is configured to extend from the left and right ends 111, 112 width-wise across the wearer’s face. The nozzle 105 comprises an air outlet at a central 25 region approximately mid-way between the left and right ends 111, 112, to be positioned approximately directly in front of and facing the wearer’s lower nasal and mouth region, in use. The nozzle 105 thus functions to duct filtered airflows from the fan assemblies 103, 104, supported at the sides of the wearer’s head, to the central outlet of the nozzle 105, and for discharging the airflows therefrom towards the lower nasal 30 and mouth region of the wearer’s face. In use, when the fan assemblies 103, 104 are attached to the ear cups 107, 108 respectively, the headgear 102 thereby supports the nozzle 105 in front of the wearer’s face. In particular, in result of the nozzle 105 being attached to the headgear 102, via the fan assemblies 103, 104, on opposite, left and right, sides of the wearer’s head, the 5 nozzle 105 is well supported and less prone to unintended movement, e.g., vibration of the nozzle 105 in use. In comparison, coupling of the nozzle 105 to the headgear 102 at only one side of the wearer’s head, for example, at the left end 111 only, may result in a torque being exerted on the single coupling by the mass of the nozzle, and may result in excessive undesired movement of the nozzle in use. 10 Like the headband 102, the nozzle 105 is configured to be flexible in a width dimension, i.e., parallel to the width dimension of the wearer’s head, so as to allow a distance between the point of coupling of the nozzle 105 to the headgear 102 to be varied. This flexibility advantageously allows the nozzle 105 also to accommodate differing 15 distances between the fan assemblies 103, 104. This may advantageously accommodate differing distances between the ear cups 107, 108, and thus differing widths of wearers’ heads. Additionally, the flexibility of the nozzle 105 may desirably aid attachment and detachment of the fan assemblies 103, 104 to the ear cups 107, 108 respectively, as will be described in further detail with reference to later Figures. 20 In examples, the nozzle 105 is configured to not contact the wearer’s face, such that it is supported by the headgear 102 a short distance in front of the wearer’s face. This noncontact configuration may advantageously improve wearer comfort, inasmuch that the potential for skin irritation or other discomfort caused by contact of the nozzle 105 with 25 the wearer’s face is reduced. Referring next in particular to Figures 3 and 4, because the fan assemblies 103, 104 are releasably attachable to a respective one of the ear cups 107, 108 of the headgear 102, the fan assemblies 103, 104, and the nozzle 105 attached thereto, may be releasably 30 attached and detached from the headgear 102 by the wearer. In examples, the fan assemblies 103, 104 and the nozzle 105 are configured to be attachable to and detachable from the headgear as an assembly, in which the nozzle 105 remains attached to the fan assemblies 103, 104 during attachment / detachment of the fan assemblies 103, 104 to / from the headgear 102. The nozzle 105 is also releasably attachable to the fan assemblies 103, 104. LD Thus the wearer may attach the nozzle 105 to the fan assemblies 103, 104, and the fan assemblies 103, 104 to the headgear 102 when the wearer desires the provision of filtered airflow, such as when the wearer is in an environment with relatively high levels of environmental air pollution, and the wearer may detach the fan assemblies 103, 104 and / or the nozzle 105 from the headgear 102 when the filtered airflow is not desired, such as when the wearer is in an environment with relatively low levels of environmental air pollution. The headgear 102 may thus be used in the latter scenario without the fan assemblies 103, 104 attached, and thus without the additional mass and bulk of the fan assemblies 103, 104. For example, the headgear may be used by the wearer simply as headphones for audio playback. The headgear 102 and components thereof, to be described in further detail with reference to later figures, may thus have dual functionality, which may desirably reduce a perceived need for the wearer to have separate air purifying and non-air purifying headphones. 20 Because the nozzle 105 releasably attaches directly to the fan assemblies 103, 104, the combination of the fan assemblies 103, 104 and the nozzle 105 may be attached as a combination to and detached from the headgear 102 as an assembly, which may allow convenient attachment and detachment of the fan assemblies 103, 104 and nozzle 105 with respect to the headgear 102. In comparison, if the nozzle 105 were to attach to the 25 headgear 102, for example to the ear cups 107, 108, instead of directly to the fan assemblies 103, 104, the wearer may be required to separately attach and detach both the nozzle 105 and the fan assemblies 103, 104 from the headgear 102, which may be relatively inconvenient for the wearer. Additionally, because the nozzle 105 attaches directly to the fan assemblies 103, 104, rather than, for example, attaching to the ear 30 cups 107, 108 or the headgear 102 more generally, the fan assemblies 103, 104 are not required to releasably fluidly couple to the ear cups 107, 108 or the headgear 102 more generally to deliver filtered airflow to flow to the nozzle 105. Indeed, in this configuration, the nozzle 105 is not required to fluidly couple to the headgear 102 to receive the filtered airflows, and thus a risk of airflow leakage between the fan assembles 103, 104 and the nozzle 105 may be reduced. 5 The nozzle 105 is releasably attachable at left and rights ports 113, 114, as shown in Figure 3, to the respective one of the fan assemblies 103, 104. The nozzle 105 is mechanically coupled to the ports 113, 114. The nozzle 105 may be releasably attached to the fan assemblies 103, 104, for example, by magnet couplings, clips, or releasable 10 catches. Thus, the nozzle 105 may be detachable by the wearer from the fan assemblies 103, 104, for example, to facilitate ex-situ cleaning of the nozzle 105. 15 To assist the wearer with the releasable attachment of the fan assemblies 103, 104 to the ear cups 107, 108 respectively, each of the ear cups 103, 104 is provided with a male locating feature, in the form of a protruding portion 301, and each of the ear cups is provided with a corresponding female locating feature, in the form of intruding portion 302. The protruding portion 301 of each ear cup 107, 108 cooperates with the intruding portion 302 of the respective fan assembly 103, 104 to function as a locating feature. This may desirably aid correct positioning of the respective fan assembly 103, 104 20 relative to the headgear 102 during attachment of the fan assemblies 103, 104 by the wearer. Each of the ear cups 107, 108 defines a mating surface 304, that is flat and generally annular and extends around the circumference of the protruding portion 301. The fan 25 assemblies 103, 104 each similarly define a flat and generally annular mating surface 303 extending around the circumference of the intruding portion 302. The mating surfaces 303, 304 of the fan assemblies 103, 104 and the ear cups 107, 108 are arranged to contact when the fan assemblies 103, 104 are attached to the respective ear cups 107, 108, to thereby stably support the fan assemblies 103, 104 relative to the headgear 102. Referring to Figure 4, the wearable air purifier 101 is shown as part of a personal air purification system 1. The personal air purification system 1 comprises a first remote device 10 in the form of a mobile telephone, and a second remote device 20, in the form of a smartwatch. Each remote device is wirelessly communicable with a communications device 519 of the wearable air purifier 101. The communications device 519 comprises a transmitter for transmitting information to the remote device. Referring next in particular to Figures 5 and 6, in examples the fan assemblies 103, 104 are substantially like, as are the ear cups 107, 108, and also the mechanism of attachment of the fan assemblies 103, 104 to the ear cups 107, 108. Thus, for brevity, only fan assembly 104 and right ear cup 108 will be described in detail herein, on the understanding that substantially the same teachings apply to fan assembly 103 and left ear cup 107. Nozzle 105 is omitted from Figures 5 and 6 to avoid obscuring the described features. Conductors are depicted by dashed lines. The headgear 102 comprises batteries 501, 502 located in cushions of the headband 106, and conductor assembly 503 for electrically coupling the batteries 501, 502 and for electrically coupling the batteries 501, 502 to components of the ear cup 108 and the fan assembly 104. 20 25 The ear cup 108 comprises the speaker housing 504 attached to an end of the headband 106. The speaker housing 504 is substantially hollow, and defines the protruding portion 301 and the mating surface 304. The protruding portion 301 is generally frustoconical in shape, and narrows progressively in area in the direction of protrusion. The mating surface 304 is flat and generally annular, and extends around the circumference of the protruding portion 301. The speaker 505 is located in the speaker housing 504, and is supplied with electrical power by the batteries 501, 502 via the conductor assembly 503. A rear part of the speaker 505 is located within the part of the volume of the speaker housing 504 defined by the protruding portion 301. 10 15 20 25 The fan assembly 104 comprises fan housing 506 and base 507. The fan housing 506 is rotatably mechanically coupled to the base 507. Thus, the fan housing 506 may be rotated relative to the base 507. The fan housing 506 and base 507 together define intruding portion 302. The intruding portion 302 defines a generally frustoconical intrusion into the fan assembly 104, that narrows in area progressively in the direction of intrusion. Base 507 defines the mating surface 303 that is flat and generally annular, and extends around the circumference of the intruding portion 302. The fan housing 506 is hollow, and a motor driven fan 508, fan controller 509, and an air filter 510 are located therein. The motor driven fan 508 is supplied with electrical power by the batteries 501, 502 via the conductor assembly 503 and the fan controller 509. The fan housing 506 comprises inlet aperture(s) 511 and outlet aperture shown as the right port 114. The outlet aperture 114 is arranged to fluidly couple with an inlet at the right end 112 of the nozzle 105 when the nozzle 105 is attached to the fan housing 506. The base 507 of the fan assembly 104 comprises mechanical attachment features 601 for releasably mechanically coupling to a cooperating mechanical attachment feature 602 mounted to the speaker housing 504, to thereby releasably mechanically couple the fan assembly 104 to the ear cup 108. The mechanical attachment features 601, 602 are located on the mating surfaces 303, 304 of the base 507 of the fan assembly 104 and the speaker housing 504 respectively. The mechanical attachment features 601, 602 are selected to couple to adequately attach the fan assembly 104, and nozzle 105, to the ear cup 108 in use, yet allow the wearer to releasably make and break the coupling to allow the wearer to releasably attach and detach the fan assembly 104 to and from the ear cup 108. The mechanical attachment features 601, 604 could, for example, be magnet couplings, clips, releasable catches, or any other suitable releasable fastener. The mechanical attachment features 601, 602 may be configured to allow the fan assembly 104 to attach to the ear cup 108 in a rotationally static motion, i.e., such that the fan assembly 104 is not required to be rotated, in a screw action, to attach the fan 30 assembly 104 to the ear cup 108. Thus, the wearer may attach / detach the fan assemblies 103, 104, and so the nozzle 105, to the ear cups 107, 108, without rotating the fan assemblies 103, 104, and thereby avoiding rotation of the nozzle relative to the headgear. Consequently, a risk of the nozzle 105 fouling the wearer’s face, or articles such as spectacles on the wearer’s face, may be reduced. 5 The conductor assembly 503 comprises a releasable conductive coupling for releasably conductively coupling the fan assembly 104 to the ear cup 108. The releasable conductive coupling is formed by cooperating conductive contacts 603, 604 located on mating surfaces 303, 304 of the base 507 of the fan assembly 104 and the speaker housing 504 respectively. In examples, the conductive contact 603 of the fan assembly 10 104 forms a socket and the conductive contact 604 of the ear cup 108 forms a pin to be LD received in the socket to make the conductive coupling. The pin may be spring-loaded to maintain the conductive coupling between the ear cup 108 and fan assembly 104 notwithstanding a small degree of relative movement between the ear cup 108 and fan assembly 104. Where more than one conductive line is required, the releasable conductive coupling may comprise the appropriate number of pairs of conductive contacts. The conductor assembly 503 further comprises a rotatable conductive coupler 513, for rotatably conductive coupling the conductive contact 603 mounted to the base 507 with 20 the fan controller 509 mounted to the fan housing 506. The rotatable conductive coupler 513 thus conductively couples the fan controller 509 to the conductive contact 603 in a way that permits relative relation between the fan housing 506 and the base 507, whilst maintaining an electrical connection between the fan controller 509 and the batteries 501, 502. The rotatable conductor assembly 513 could, for example, comprise 25 one or more ribbon cables, or slip rings. Fan 508 is thus controllable by fan controller 509 to draw air in through inlets 511, via filter 510, and discharge the filtered airflow via the outlet (right port 114) to the nozzle 105, as described previously with reference to earlier Figures. Referring in particular to Figure 5, when the fan assembly 104 is attached to the ear cup 108, the protruding portion 301 of the ear cup 108 is accommodated in the intruding portion 302 of the fan assembly 104, such that the protruding portion 301 fills substantially the whole volume of the intruding portion 302, and the surface of the 5 protruding portion 301 contacts the surface of the intruding portion 302. In this attached condition, the mating surface 303 of the fan assembly 104 is in contact with the mating surface 304 of the ear cup 108. LD 20 The rotation of the fan housing 506 relative to the base 507 rotation may desirably allow the wearer to rotate the nozzle 105 relative to the headgear 102 when the fan assemblies 103, 104 are attached to the ear cups 107, 108, as will be described in further detail with reference to later Figures. In particular, because the fan housing 506 is rotatable relative to the base 507, this rotation of the nozzle 105 relative to the headgear 102 may be achieved despite the base 507 being rotationally static relative to the ear cup 108. Consequently, the mechanical fastening features 601, 602 and the conductive coupling contacts 603, 604, are not required to accommodate rotation of the base 507 relative to the ear cup 108. Rather, the mechanical fastening features 601, 602, and the conductive coupling parts 603, 604 need only accommodate static releasable attachment of the fan assembly 104 to the ear cup 108. Thus, the mechanical fastening features 601, 602, and the conductive coupling parts 603, 604 may be simplified. Ear cup 108 further comprises an alert system 514 located in the speaker housing 504. Alert system 514 is provided to monitor an environmental condition and alert the wearer if the monitored environmental condition is unacceptable and the fan assembly 104 is 25 detached from the ear cup 108 and / or if the nozzle 105 is detached from the fan assembly 104. Thus, the wearer may be prompted to attach the fan assembly 104 to the headgear 102 and / or attach the nozzle 105 to the fan assembly 104, so that the wearer may receive the filtered airflow to counter the unacceptable environmental condition. 30 The alert system 514 comprises fan assembly sensor 515, nozzle sensor 518 (see Figures 3, 5 and 6), environmental condition sensor 516, and controller 517. The controller may be referred to as an alert signal generator. Each fan assembly 103, 104 comprises a nozzle sensor 518, even though the nozzle sensor 518 associated with the right fan assembly 104 is shown and labelled in Figures 5 and 6. The alert system 514 comprises an alert indicator in the form of the speaker 505. 5 The controller 517 generates an alert signal on the basis of the environmental condition sensor 516 sensing that an environmental condition meets a threshold, and the nozzle sensor 518 indicating the nozzle 105 is unattached to the fan assembly 104. The alert system 514 communicates the alert signal to the speaker 505 and, on receipt of the alert 10 signal, the speaker 505 generates a sound to be heard by the wearer. The sound may be a specific sound associated with an alert to prompt the wearer to attach the nozzle 105 with the fan assembly 104 to the ear cup 108, or, if the fan assembly 104 is already attached, to attach the nozzle to the fan assembly 104. 15 The nozzle sensor 518 as described above is arranged to detect attachment of the nozzle 105 to the apparatus 101 at the right port 114 by means of a Hall effect sensor configured to detect a detectable member, in the form of a magnet, of the nozzle 105. The communications device 519, shown in Figure 4, can be used to alert the wearer by 20 communicating with one of the remote devices 10, 20. For example, the communications device 519 may send the alert signal, in the form of a push notification, to one of the remote devices 10, 20 to visibly alert the wearer and prompt the wearer to attach the nozzle 105. In such instances, it is at least one of the remote devices 10, 20 that comprises the alert indicator. 25 The fan assembly sensor 516 is to sense if the fan assembly 104 is attached to the ear cup 108. The fan assembly sensor 516 is located on the mating surface 304 of the speaker housing 504, and is arranged to interact with the mating surface 303 of the fan assembly 104 when the fan assembly 104 is attached to the ear cup 108. Thus, the fan 30 assembly sensor 515 can be interrogated by the controller 517 to determine if the fan assembly 104 is attached to the ear cup 108. For example, the fan assembly sensor 515 could comprise a momentary switch arranged to be depressed by the fan assembly 104 when the fan assembly 104 is attached to the speaker housing 108. The nozzle sensor 518 is to sense if the nozzle 105 is attached to the fan assembly 104. 5 The nozzle sensor 518 is located on the fan assembly 104 adjacent the right port 114 and is arranged to interact with the end of the nozzle 105 when the fan assembly 104 is attached to the ear cup 108. Thus, the nozzle sensor 512 can be interrogated by the controller 517 to determine if the nozzle 105 is attached to the fan assembly 104. For example, the nozzle sensor 518 could comprise a momentary switch arranged to be 10 depressed by the nozzle 105 when the nozzle 105 is attached to the fan assembly 104. The environmental condition sensor 516 is to sense an environmental condition. The environmental condition sensor is exposed to ambient air via apertures in the speaker housing 504. The environmental condition sensor could, for example, be sensitive to one or more pollutant gases in the ambient air, such as, nitrogen dioxide or another pollutant gas in ambient air, or to particulate matter, such as PM2.5 sized particulates. 20 25 The controller 517 is configured to interrogate the fan assembly sensor 515 to sense if the fan assembly 104 is attached to the ear cup 108 and / or interrogate the nozzle sensor 518 to sense if the nozzle 105 is attached to the fan assembly 104, interrogate the environmental condition sensor 516 to sense the particular environmental condition of interest, and then selectively generate a wearer-perceptible alert to the wearer if the fan assembly 104 is not attached to the ear cup 108 and / or the nozzle 105 is not attached to the fan assembly 104, and if the sensed environmental condition meets a particular criteria. For example, the controller 517 could comprise one or more predefined threshold values representing threshold environmental condition levels considered to be unacceptable to the wearer, for example, threshold pollutant gas concentration levels. In this case, if the sensed environmental condition meets, for example, equals or surpasses (for example, exceeds) the threshold value, and the fan assembly 104 is not attached to the ear cup 108 and / or the nozzle 105 is not attached to the fan assembly 104, the alert system may generate a wearer-perceptible alert, to thereby prompt the wearer to attach the fan assembly 104 to the ear cup 108 and / or attach the nozzle 105 to the fan assembly 104. Thus, in a scenario where the wearer is wearing the headgear 102 without the fan 5 assembly 104 attached to the headgear 102 or without the nozzle 105 attached to the fan assembly 104, but the environmental condition is determined to meet the predefined threshold, the wearer can be alerted to the environmental condition to thereby prompt the wearer to attach the fan assembly 104 to the headgear 102 or attach the nozzle 105 to the fan assembly 104, to receive filtered airflow to thereby counter the environmental 10 condition. Referring next in particular to Figures 7 and 8, because of the previously described rotation of the fan housing 506 relative to the base 507 of the fan assemblies 103, 104, the nozzle 105 may be rotated relative to the headgear 102 in use. This may desirably 15 enable the nozzle position to be adjusted relative to the headgear to suit different head sizes. Further, referring in particular to the configured depicted in Figure 8, this rotation may allow the nozzle to be rotated by the wearer away from the lower nasal / mouth region to a lowered position. This lowered position may usefully allow the wearer to move the nozzle away from their mouth, which may, for example, be desirable when the 20 wearer is conversing with another person, eating or drinking. A second wearable air purifier 201, embodying aspects of the present disclosure, is shown schematically in Figures 11 and 12. Features of the second wearable air purifier 201 are the same as the first wearable air purifier 101 described previously, and 25 only the differences are discussed in detail. Like features are given numerals increased by 100. The second wearable air purifier 201 comprises a headgear 202, a left fan assembly 203, a right fan assembly 204, and a nozzle 205. The headgear 202 comprises a headband 30 206 and left and right ear cups 207, 208 connected to respective ends of the headband 206. The ear cups 207, 208 comprise respective annular cushions 209, 210 for cushioning against the wearer’s head. The left and right ear cups 207, 208 comprise respective speaker housings (right speaker housing 604 is illustrated in Figure 11) for housing components, such as respective speakers, as with the first wearable air purifier 101. Differently to the first wearable air purifier 101, the headgear 202 of the second wearable air purifier 201 comprises the fan assemblies 204, 205, such that the fan assemblies 204, 205 of the second wearable air purifier 201 are unattachable from the left and right ear cups 207, 208 (as opposed to being releasably attachable in the first 10 wearable air purifier 101). The nozzle 205 of the second wearable air purifier 201 is attachable at left and right ends 211, 212 to a respective one of the left and right ear cups 207, 208 (rather than the fan assemblies, as with the first wearable air 15 purifier 101). The nozzle 205 is releasably attachable at left and rights ports 213, 214, as shown in Figure 11, to the respective one of the left and right ear cups 207, 208. The nozzle 205 is mechanically coupled to the ports 213, 214 of the ear cups 207, 208. The nozzle 205 may be releasably attached to the ear cups 207, 208, for example, by magnet couplings, clips, or releasable catches. Thus, the nozzle 205 may be detachable by the wearer from 20 the ear cups 207, 208, for example, to facilitate ex-situ cleaning of the nozzle 205. Ear cup 208 further comprises an alert system 614 located in the speaker housing 604. The alert system 614 of the second wearable air purifier 201 performs in the same manner as the alert system 514 of the first wearable air purifier 101, except that the fan 25 assemblies are no longer releasably attachable in the second wearable air purifier 201. Therefore, functionality specific to the releasably attachable fan assemblies of the first wearable air purifier 101 do not apply to the second wearable air purifier 201. The alert system 614 comprises nozzle sensor 618 which functions in the same manner as described for the first wearable air purifier 101. Referring next to Figure 9, in examples, the controller 517 of alert system 514 comprises input / output device 901, memory 902, processor 903, and system bus 904. The controller 517 of the alert system 514 is configured to generate the wearer-5 perceptible alert in dependence on whether the fan assembly 104 is attached to the headgear 102, sensed by fan assembly sensor 515, and on whether an environmental condition, sensed by environmental condition sensor 516, meets a threshold. The alert system 514 could, for example, utilise the speaker 505 to generate an audible alert to the wearer. The alert system could, for example, further send a signal to the fan controller 10 509 to vary the rate of airflow generated by the fan 508 in dependence on the sensed environmental condition. Thus, the airflow rate generated by the fan 508 may be varied to counter the environmental conditions. 15 Input / output interface 901 is provided for connection of the fan assembly sensor 515, nozzle sensor 518, the environmental condition sensor 516, the batteries 501, 502, the speaker 505, and the fan controller 509. Input / output interface 901 could further comprise a radio communication device configured to output a radio signal for receipt by a remote device. Memory 902 stores a computer program, comprising machine-readable instructions, for interrogating the fan assembly sensor 515 and the 20 environmental condition sensor 516, and for generating an alert signal and / or a signal to the fan controller 509. Memory 902 further stores one or more predefined environmental condition threshold values, representing environmental conditions considered unacceptable to the wearer. Processor 903 is configured for receiving and processing signals from the fan assembly sensor 515, the nozzle sensor 518, and the 25 environmental condition sensor 516, sense if the fan assembly 104 is attached to the headgear and / or sense if the nozzle 105 is attached to the fan assembly 104, and based on a signal from the fan assembly sensor 515 and / or the nozzle sensor 518, sense the environmental condition using the environmental condition sensor 516, determine if the sensed environmental condition meets the threshold value stored in memory 902, and 30 subsequently generate an alert signal if the sensed environmental condition is determined to meet the threshold. The processor 903 is thus an alert signal generator. The components 901 to 903 of the controller are in communication via system bus 904. Referring finally to Figure 10, in examples the computer program for generating the 5 alert and controlling the airflow rate of the fan 508, based on the signals from the fan assembly sensor 515 and / or the environmental condition sensor 516 comprises six stages. At stage 1001, the computer program causes the processor 903 to initiate the alerting 10 procedure. The initiation stage could be triggered, for example, by a wearer’s input, such as wearer pressing an ‘ON’ button connected to the input / output interface 901 of the controller 517, or by a wearer beginning to use the headgear for audio playback and thus energising the speaker 505. 15 At optional stage 1002, the computer program causes the processor 903 to interrogate the fan assembly sensor 515 to determine if the fan assembly 104 is attached to the ear cup 108. If the determination is that the fan assembly 104 is attached to the ear cup 108, the process may cease, and stage 1001 may subsequently be repeated periodically. If the determination is that the fan assembly is not attached to the ear up 108, the 20 process may proceed to stage 1003. Stage 1002 does not apply to the second wearable air purifier 201 because the pair of fan assemblies 203, 204 are not detachable, at least in in normal use. At stage 1003, the computer program causes the processor 903 to interrogate the nozzle 25 sensor 518 to determine if the nozzle 105 is attached to the fan assembly 104. If the determination is that the nozzle is attached to the fan assembly 104, the process may cease, and stage 1001 may subsequently be repeated periodically. If the determination is that the nozzle 105 is not attached to the fan assembly 104, the process may proceed to stage 1004. At stage 1004, the computer program causes the processor 903 to interrogate the environmental condition sensor 516 to sense the environmental condition. At stage 1005, the computer program causes the processor 903 to retrieve the threshold 5 environmental condition threshold value from memory 902, compare the environmental condition sensed at stage 1003 to the threshold value retrieved from memory 902, and determine if the sensed environmental condition meets the threshold value. If the determination is that the sensed environmental condition does not meet the threshold, e.g., is less than the threshold, the process may cease, and stage 1001 may subsequently 10 be repeated periodically. If the determination is that the environmental condition does meet the threshold, e.g., is equal to or greater than the threshold, the process may proceed to stage 1006. 15 At stage 1006 the computer program causes the processor 903 to generate an alert signal and / or a fan speed signal. Stage 1006 could, for example, involve the processor 903 outputting an alert signal to the speaker 505, via input / output device 901, to thereby cause the speaker 505 to generate an acoustic noise to alert the wearer. Stage 1006 could, for example, further involve the processor 903 outputting a fan speed signal to the fan controller 509, via input / output interface 901, to thereby cause the fan controller 20 509 to set the airflow rate of the fan 508 to a relatively high rate, to thereby counter the environmental condition. The operations of stages 1002 to 1006 could be performed in various alternative orders. For example, the operations of stage 1002 could be performed after the operations of 25 stages 1003 and 1004, and / or the operations of stage 1004 could be performed before the operations of stage 1003, etc. Stage 1006 could involve generating one or both of the fan alert signal and the fan speed signal. And stages of the process could be repeated. For example, after stage 1006, stages 1002 and / or 1003 could be repeated, to check whether the wearer has actually complied with the alert to attach the fan assembly 30 to the headgear and / or the nozzle to the fan assembly. If this further stage is answered in the negative, the alert system could repeat stage 1006, and generate a further alert signal, to further remind the wearer to attach the fan assembly to the headgear and / or the nozzle to the fan assembly. Further, stage 1006 could involve outputting the alert signal via a radio communication device, for example, a radio communication device incorporated in input / output device 901, for wireless radio transmission of the alert 5 signal to a remote device, for example, to a wearer’s smartphone. In some examples, the nozzle sensor 518 is configured to detect the nozzle 105 by an RGB sensor. In some examples, the nozzle sensor 518 is configured to detect the nozzle sensor 518 at both ports 113, 114. In further examples, the nozzle sensor 518 is 10 arranged to detect the nozzle 105 at a different number of different locations. 20 25 In some examples, the nozzle sensor 518 is configured to detect the nozzle 105 by an optical sensor arranged to detect a colour of the currently attached nozzle 105. In other examples, a different optical property of the nozzle 105 may be detected, for example, reflectance. In yet further examples, the nozzle sensor 518 may include other sensors. In some examples, the nozzle sensor 518 includes a sensor configured to detect a physical property associated with the nozzle 105, for example, to measure a distance to a reference portion of the nozzle 105. In some examples, the nozzle sensor 518 includes a reader configured to detect a machine-readable code comprised by the nozzle 105, for example, a barcode or a QR code or an RFID tag. The reader may be an NFC reader arranged to read an RFID tag of the nozzle 105. In some examples, the nozzle sensor 518 includes a sensor configured to detect an orientation or position of the nozzle 105 relative to the wearable air purifier 101, for example the headgear 102. For example, the nozzle sensor 518 may include a 3-axis magnetometer configured to detect a magnetic orientation or positioning of the nozzle 105 relative to the wearable air purifier 101, for example the headgear 102. In some examples, the nozzle is releasably attached to the fan assembly, which is fixedly attached to the headgear. In other examples, the nozzle and the fan assembly may be removable together from the headgear. Accordingly, in a more general sense, the nozzle may be said to be releasably attached to the headgear. Moreover, the nozzle sensor may be said to sense the presence or absence of the nozzle and that this may be done directly or indirectly. For example, the nozzle sensor may sense the absence or presence of the fan assembly and then use this information to determine if the nozzle is attached or detached from the headgear. 21 03 25

Claims

1. A wearable air purifier, comprising:a headgear for wearing on a wearer’s head;5 a fan assembly operable to generate filtered airflow,a nozzle for receiving the filtered airflow generated by the fan assembly, and for discharging the filtered airflow towards the wearer’s face, wherein the nozzle is releasably attachable to the headgear or the fan assembly;an alert system for generating an alert signal for use in prompting the wearer to 10 attach the nozzle, the alert system comprising:a nozzle sensor to sense if the nozzle is attached to or detached from the headgear or the fan assembly;an environmental condition sensor for sensing an environmental condition; andan alert signal generator for generating the alert signal on the basis of the environmental condition sensor sensing the environmental condition meets a criterion, and the nozzle sensor indicating the nozzle is unattached to the headgear or the fan assembly.The wearable air purifier according to claim 1, comprising an alert indicator, wherein the alert system is configured to communicate the alert signal to the alert indicator and, on receipt of the alert signal, the alert indicator indicates an alert to the wearer.25 3. The wearable air purifier according to claim 2, wherein the alert indicatorindicates by generating audible, haptic or visual feedback to the wearer.

4. The wearable air purifier according to claim 3, wherein the alert indicator comprises a speaker system supported by the headgear, wherein the alert system is 30 configured to communicate the alert signal to the speaker system, wherein the alert signal is transmitted as audible feedback to the wearer.

5. The wearable air purifier according to preceding claim, wherein the alert system is configured to generate a further alert signal if the nozzle remains unattached to the headgear.

56. The wearable air purifier according to any preceding claim, further comprising a fan controller for controlling operation of the fan assembly, wherein, following generation of the alert signal, the fan controller is configured to cause the fan assembly to generate the filtered airflow on the basis of the nozzle sensor indicating the nozzle is 10 attached to the headgear or the fan assembly.

7. The wearable air purifier according to any preceding claim, wherein the alert15system comprises a detectable member, and the nozzle sensor comprises a proximity sensor for sensing a presence of the detectable member that is indicative of the nozzle being attached to the headgear or the fan assembly.

8. The wearable air purifier according to claim 7, wherein the detectable member comprises a magnet, and the proximity sensor comprises a Hall effect sensor.20 9. The wearable air purifier according to any preceding claim, wherein theenvironmental condition is indicative of air quality in an environment surrounding the wearable air purifier.

10. The wearable air purifier according to any preceding claim, wherein the 25 environmental condition is indicative of a concentration of particulate matter, such as PM2.5 sized particles, in an environment surrounding the wearable air purifier.

11. The wearable air purifier according to any of preceding claim, wherein the fan assembly is fixedly attached to the headgear.

12. The wearable air purifier according to any one of claim 1 to claim 10, wherein the fan assembly is releasably attachable to the headgear.

13. The wearable air purifier according to claim 12, wherein the wearable air 5 purifier comprises:a fan assembly sensor;wherein the alert signal is generated on the basis of the environmental condition sensor sensing the environmental condition meets the criterion, the nozzle sensor indicating the nozzle is unattached to the fan assembly, and the fan assembly sensor 10 indicating the fan assembly is unattached to the headgear.

14. The wearable air purifier according to claim 12 or claim 13, wherein the nozzle15is fixedly attached to the fan assembly.

15. The wearable air purifier according to any preceding, wherein the headgear comprises the nozzle sensor.

16. The wearable air purifier according to any one of claim 1 to 13, wherein the fan assembly comprises the nozzle sensor.2017. The wearable air purifier according to any preceding claim, wherein the headgear comprises the alert signal generator.

18. The wearable air purifier according to any preceding claim, wherein the 25 headgear comprises the environmental condition sensor.

19. The wearable air purifier according to any preceding claim, wherein the alert system comprises a transmitter for transmitting the alert signal to a remote device, remote from the wearable air purifier, in response to the generation of the alert signal.

20. A personal air purification system comprising:a wearable air purifier, comprising:a headgear for wearing on a wearer’s head;a fan assembly operable to generate filtered airflow; anda nozzle for receiving the filtered airflow generated by the fan assembly, 5 and for discharging the filtered airflow towards the wearer’s face, wherein thenozzle is releasably attachable to the headgear or the fan assembly;a remote device communicable with the wearable air purifier; andan alert system for generating an alert signal for use in prompting the wearer to attach the nozzle, the alert system comprising:a nozzle sensor, comprised by the wearable air purifier, to sense if the nozzle is attached to or detached from the headgear or the fan assembly;an environmental condition sensor, comprised by the wearable air purifier and / or the remote device, for sensing an environmental condition; andan alert signal generator, comprised by the wearable air purifier or the remote device, for generating the alert signal on the basis of the environmental condition sensor sensing the environmental condition meets a criterion, and the nozzle sensor indicating the nozzle is unattached to the headgear or the fan assembly.20 21. The personal air purification system according to claim 20, comprising:an alert signal indicator configured to generate feedback, such as audible, haptic or visual feedback, to the wearer, on the basis of the generated alert signal;wherein the wearable air purifier and / or the remote device comprises the alert signal indicator.2522. A method of prompting a wearer of a wearable air purifier to attach a nozzle to a headgear or a fan assembly to generate filtered airflow by the fan assembly and discharge the filter airflow towards the wearer’s face by the nozzle, wherein, when the nozzle is unattached to the headgear or the fan assembly and an environmental 30 condition meets a criterion on the basis of an environmental condition sensor sensingthe environmental condition, the method comprises generating an alert signal to prompt the wearer to attach the nozzle.

23. The method according to claim 22, comprising activating the fan assembly when 5 the nozzle is attached to the headgear or the fan assembly to generate filtered airflow and discharge the filtered airflow from the nozzle towards the wearer’s face.

24. The method according to claim 22 or claim 23, wherein the fan assembly is releasably attachable to a headgear of the wearable air purifier, and the generating the 10 alert signal comprises generating the alert signal to prompt the wearer to attach the nozzle to the headgear or the fan assembly and the fan assembly to the headgear.21 03 25

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