Alarm sensor for a window or a door and method of operating an alarm sensor

Abstract

The invention relates to an alarm sensor for a window or a door, comprising a magnetic detector, a shock / movement detector, and a microphone. The invention further relates to a method of operating a sensor as defined in any one of the preceding claims in an alarm installation, the alarm installation comprising a central unit, the method comprising the step of activating the microphone in response to a trigger signal.

Description

[0001] Alarm sensor for a window or a door and method of operating an alarm sensor

[0002] The invention relates to an alarm sensor for a window or a door, and to a method of operating an alarm sensor of an alarm installation.

[0003] Alarm installations are used for monitoring premises / buildings and typically provide a means for detecting the presence and / or actions of people at the premises, and reacting to detected events. Commonly such alarm installations include alarm sensors to detect the opening and closing of doors and windows, movement detectors to monitor spaces for signs of movement, microphones to detect sounds such as breaking glass, and image sensors to capture still or moving images of monitored zones. Such alarm installations may be self-contained, with alarm indicators such as sirens and flashing lights that may be activated in the event of an alarm condition being detected. Such installations typically include a central unit that is coupled to the sensors, detectors, cameras, etc. (“nodes”), and which processes received notifications and determines a response. The central unit is typically linked to the various nodes wirelessly, rather than by wires, since this facilitates installation and provides some safeguards against sensors / detectors effectively being disabled by disconnecting them from the central unit. Similarly, for ease of installation and to improve security, the nodes of such alarm installations are typically battery rather than mains powered.

[0004] Alternatively, an alarm installation may include an installation at a premises, domestic or commercial, that is linked to a remote monitoring centre where typically human operators manage the responses required by different alarm and notification types. In such centrally monitored alarm installations, the central unit at the premises installation typically processes notifications received from the nodes in the installation, and notifies the remote monitoring centre of only some of these, depending upon the settings of the alarm installation and the nature of the detected events. In such a configuration, the central unit at the installation is effectively acting as a gateway between the nodes and the remote monitoring centre.

[0005] In both centrally-managed and self-contained alarm installations one of the most important issues, from a practical perspective, is the battery life of the nodes of the installation - that is, the battery life of the various detectors, sensors, cameras. Obviously, if a node’s battery loses sufficient power, the node may be unable to sense a change of state or to contact the central unit, and consequently the security installation develops a weak spot where an intruder may gain access to the premises undetected. For centrally-managed alarm installations it is usually the responsibility of the company running the alarm installation, rather than the premises owner or occupier, to change batteries, and obviously the shorter the battery life in nodes, the more frequently site visits need to be made and the greater the administrative cost. Consequently, controlling power consumption in the nodes is a high priority.

[0006] Further, a very important issue for every alarm installation is a reduction of false alarms, or a means to distinguish between an incident and a false alarm when an event occurs which triggers one of the nodes.

[0007] The object of the invention is to provide means for reducing false alarms.

[0008] In order to solve this object, the invention provides an alarm sensor for a window or a door, comprising a magnetic detector, a shock and / or movement detector, and a microphone. The microphone allows capturing audio signals when the alarm sensor is being triggered by the magnetic detector (indicating that the door or window is being opened) or by the shock / movement detector (indicating mechanical impact on or movement of the glass, the window or the door). The audio signal provides “context information” which allows an easier distinction between a false alarm and a critical situation.

[0009] Preferably, the sensor comprises a tamper detector which allows capturing an audio signal when there is an attempt to manipulate the alarm sensor.

[0010] In an embodiment, the shock / movement detector of the alarm sensor comprises at least one of a piezo shock / vibration detector and an accelerometer. Both devices are advantageous in that they require a very small amount of electric energy so that a long battery lifetime is achieved.

[0011] Preferably, the sensor includes a receiver and a transmitter for communicating with another device, optionally with a central unit of an alarm installation so that either the entire audio signal in the form of an audio clip or specific information on the recorded audio signal can be transmitted to the central unit (and possibly from the central unit to a remote monitoring centre).

[0012] In one embodiment, the sensor is configured (i) to process signals from the magnetic detector and from the shock / movement detector in order to detect opening and / or breach of the door or window, and to generate an event detection trigger signal, (ii) to process a signal from the microphone to provide contextual information regarding the detected event.

[0013] The detected opening and / or breach may also include, in the context of the present disclosure, an event of potential opening and / or breach of the door or window. That is to say, signals from, e.g., the magnetic detector, the shock / movement detector, may correspond to those measured in an event that may potentially be the opening and / or breach of the door or window, with such event being the actual opening and / or breach or not, i.e., a false alarm event.

[0014] The sensor is configured to be surface mounted to a movable or fixed part of a door or window, optionally independently of a locking mechanism of the door or window. This allows adding the sensor to already existing windows and doors with less effort.

[0015] In order to solve the above object, the invention further provides a method of operating an alarm sensor of an alarm installation as defined above, the alarm installation comprising a central unit, the method comprising the step of activating the microphone in response to a trigger signal. The trigger signal ensures that the audio signal is recorded only if there is “a need” such as suspicious activity which is detected by the alarm sensor or possibly by any other node of the alarm installation (such as a PIR or a camera), thereby increasing the battery lifetime.

[0016] In an embodiment, the trigger signal originates from at least one of the magnetic detector, the shock / movement detector, and the tamper detector. In other words, the alarm sensor activates the microphone when suspicious activity is being detected by the alarm sensor itself.

[0017] In another embodiment, the trigger signal originates from the central unit. This allows capturing an audio signal from alarm sensors other than the one which has triggered an alarm, in order to obtain more information for assessing the nature of the incident. The installation has a disarmed state, and at least one armed state, wherein the trigger signal is generated only when the installation is an armed state. This ensures a long battery life.

[0018] In one embodiment, the alarm installation comprises a transceiver for communicating via a data connection with a remote monitoring centre, the method comprising the step of providing to the sensor a trigger signal originating from the remote monitoring centre. It is thus possible for an operator at the remote monitoring centre to collect and consider additional audio signals for putting him / her in a position to better assess the nature of the incident once an alarm has been triggered.

[0019] According to an aspect of the invention, the audio signal is classified by a classification device, optionally within the sensor or within the central unit. Classifying the audio signal is advantageous in that only the classification data has to be sent to the central unit in the first place, thereby saving transmission time and battery life. Should there be the need for a user of the alarm installation or an operator at the remote monitoring centre to listen to the entire audio clip, it can be uploaded by the alarm sensor upon receiving a specific request.

[0020] Preferably, the audio clip is automatically deleted after a predefined time period has lapsed. This ensures that data privacy requirements are met and that a small memory for recording the audio signal is sufficient in the alarm sensor.

[0021] It is also possible that a deletion signal is transmitted to the alarm sensor so that the audio clip is deleted after an alarm situation has been cleared.

[0022] The invention will now be described with reference to the enclosed drawings. In the drawings,

[0023] - Figure 1 schematically shows an alarm installation,

[0024] - Figure 2 schematically shows an alarm sensor used in the alarm installation of Figure 1 , and

[0025] - Figure 3 is a schematic flow diagram illustrating various functions and information flows during operation of the alarm installation, for example, at a sensor of Fig. 2, a central unit, and a remote monitoring centre. In Figure 1 , reference numeral 1 designates an example building to be protected with an alarm installation. The building 1 can, for example, be a house, an apartment in the house, or a small business building.

[0026] The building 1 comprises a door 3 and a plurality of windows 4.

[0027] Associated with the door 3 and one or more (for example, each) of the windows 4 is an alarm sensor 10 which is part of an alarm installation. The alarm installation is adapted for detecting an unauthorized intrusion or an attempt of unauthorized intrusion.

[0028] The alarm sensor 10 is mounted on at least one of the movable parts or fixed parts of the door or window, for example, a door leaf or door frame or on a window leaf or a window sash or a window frame. A magnet 12 may be mounted on the other of the movable or fixed parts.

[0029] The alarm installation comprises a central unit 14 which can communicate (typically via a wireless communication such as power-efficient transceivers in the frequency band between 862 MHz and 870 MHz, or LTE cat M) with each of the alarm sensors 10. To this end, central unit 14 comprises a transceiver 16. Dashed lines symbolize the wireless communication.

[0030] The alarm installation can further comprise at least one camera 18 which also communicates with the central unit 14. Although not shown, the alarm installation may also include other peripherals, for example, a motion detector (e.g. a passive infra-red detector), a keypad, a video-doorbell, and / or an obfuscation cloud generator (e.g. for hindering visibility and thus urging an intruder to leave).

[0031] The central unit 14 is connected to a remote monitoring centre 20 also via a wireless and / or wired communication means. An internet connection or, as a fallback means, a cellular connection, can be used. The term “remote monitoring centre” may include one or more centres manned by human operators responsible for reacting to alarms, and / or one or more data processing centres, whether or not such centres are located on the same site as one another.

[0032] In an alternative embodiment, the central unit 14 may be omitted at the installation, and the or each alarm sensor 10 (and optionally the camera 18) may communicate independently with a remote monitoring centre 20, for example, via cellular wireless data communication, for example, LTE cat M communication.

[0033] In Figure 2, details of the alarm sensors 10 are shown.

[0034] The alarm sensor 10 comprises a microcontroller 30, and a power supply 42. In some forms, the sensor 10 comprises at least one detector for sensing a physical condition that is affected by opening and / or breach of the window or door. The at least one detector may include a magnetic detector 32, and a shock / movement detector 34. Additionally or alternatively, the sensor 10 comprises a microphone 36 and a memory 38.

[0035] Further, the alarm sensor 10 comprises a tamper detector 40.

[0036] Still further, the alarm sensor 10 comprises indicator lights 44 (preferably LEDs), and a wireless transceiver 46 (e.g. comprising a wireless transmitter and / or a wireless receiver).

[0037] The microcontroller 30 controls functionality of the alarm sensor 10.

[0038] The magnetic detector 32 is adapted to generate a signal when its position with respect to the magnet 12 changes, in particular to indicate that the door 3 or the window 4 is being opened. To this end, the magnetic detector 32 can comprise a hall sensor, a reed switch, or a magnetometer, e.g. multi-axis (e.g. 3-axis) magnetometer.

[0039] The shock / movement detector 34 is adapted to generate a signal when there is a movement of the door or window, and / or when there are vibrations in the door / window. To this end, shock / movement detector 34 can comprises a piezo shock / vibration detector, or an accelerometer.

[0040] The microphone 36 is adapted to capture audio signals which are then recorded / stored as an audio clip in the memory 38. Memory 38 can in particular be a flash memory.

[0041] The tamper detector 40 is adapted for detecting an attempt to manipulate, remove or otherwise make the alarm sensor 10 inoperable. It can comprise electric contacts which are arranged so as to change state (for example, be interrupted) when a housing of the alarm sensor 10 is opened or when there is an unauthorized attempt to cut of the power supply of the alarm sensor 10.

[0042] The power supply 42 comprises a battery or a plurality of batteries which can be replaced when necessary.

[0043] The indicator lights 44 can provide an indication to the user that the alarm sensor 10 operates properly, e.g. by flashing a green light at specific intervals, or can provide an indication that there is a malfunction, e.g. by flashing a red light at specific intervals.

[0044] The transceiver 46 provides for bi-directional communication with the central unit 14.

[0045] The alarm sensor 10 is housed within a case that is configured for surface mounting to the window or door, for example, by adhesive or by one or more fixings, for example, screws. The alarm sensor 10 can be configured for mounting to the window or door independently of a locking mechanism for the window or door. Such an example is distinct from the locking mechanism, which may provide a degree of sensor independence sensitive to intrusion attempts whether or not the intrusion attempts focus on the locking mechanism or other regions of the door or window.

[0046] Referring to Figures 2 and 3, the alarm installation and the alarm sensor 10 can be operated as follows:

[0047] Upon receipt of an audio capture trigger signal (S1 ; S2; S3), also referred to below as merely a trigger signal, the microphone 36 captures (S4) audio signals for a predetermined period of time. As the lifetime of the power supply 42 is an important aspect of the alarm sensor 10, the audio signals are captured for a short period of time only. As examples, the audio signal is captured for five or ten seconds.

[0048] The audio signal is stored (S4) as an audio clip in the memory 38.

[0049] The audio data may be compressed during recording for storage, and / or compressed for uploading. The trigger signal can be of one or more, optionally any, of the following different origins.

[0050] In one embodiment, the trigger signal (S1) originates from the alarm sensor 10. In particular, the trigger signal (S1) can be the result of the magnetic detector 32 and / or the shock / movement detector 34 generating a signal which indicates that the door 3 or window 4 is being opened, or can be the result of the shock / movement detector 34 generating a signal which indicates that there is a vibration in the door / window, or that somebody is banging on the door / window. The trigger signal can also be the result of the tamper detector 40 generating a signal which indicates that there is an attempt to tamper with the alarm sensor 10.

[0051] Additionally or alternatively, the trigger signal (S2) originates from the central unit 14. The trigger signal can be sent in response to one of the plurality of alarm sensors 10 sending an alarm signal (S5) (as an indication that there is activity which is at least suspicious), or in response to a signal sent from the camera 18, indicating that there is movement somewhere within the building at a place where movement is not expected.

[0052] Additionally or alternatively to either of the above, the trigger signal (S3) originates from the remote monitoring centre 20. The trigger signal can be sent by personnel of the remote monitoring centre 20 in a situation in which the personnel notices suspicious activity in the building 1 because of an alarm notification signal (S6) sent from the central unit 14, and commands or requests an audio clip to be recorded by one particular alarm sensor 10 or by a plurality of alarm sensors 10, to provide additional context for helping clarify if there is a false alarm or if there is a true alarm situation.

[0053] The alarm installation may have, or be set in, a disarmed state, or at least one armed state. For the current embodiments, the trigger signal is preferably generated only when the alarm installation is in an armed state. This is advantageous in order to reduce the power consumption of the alarm sensors 10 (and thus to increase the lifetime of the batteries) and with respect to privacy laws and occupant privacy.

[0054] The armed state of the alarm installation can be one of an “armed-away” state (which is the state when no occupants are in the building so that there is a level of maximum protection), and an “armed at home” state (which is the state when occupants are in the building but have defined areas which are unoccupied so that these areas and the perimeter of the building are monitored by the alarm installation). In the “armed-away” state, potentially each and every of the alarm sensors 10 can be used for recording an audio clip, while in the “armed at home” state, only those alarm sensors 10 which are in areas supposedly unoccupied can be used for recording an audio clip.

[0055] In other words, the alarm sensors 10 are authorized to record an audio clip only in an armed state. In a disarmed state, there is no recording of an audio clip.

[0056] In one embodiment, the central unit 14 transmits (S7) the arm state (or changes to the arm state) to the alarm sensors 10. The sensors are authorised to self-record when in an armed state.

[0057] In another embodiment, the alarm sensors 10 behave the same way whether the alarm installation is armed or disarmed, and always transmit basic alarm triggers (S5) to the central unit 14 whether armed or disarmed. However, the alarm sensors 10 will only record audio when the central unit 14 (which knows the arm / disarmed state) authorises or commands (S8) audio recording. This requires a two-way exchange of information between the alarm sensors 10 and the central unit 14 for each trigger event. The sensor 10 is responsive to a command signal (S2) received via the transceiver, to record an audio clip.

[0058] In the current examples, an audio signal itself is not a trigger, as continuously monitoring and processing audio may consume battery power excessively. Instead, a low power trigger is used, which can be a movement signal (S1 ; S4) detected by the magnetic sensor or by the vibration / movement sensor, or a vibration signal (S1 ; S4) detected by a piezo shock detector, or a specific recording command signal (S2) sent by the central unit 14.

[0059] Should an audio clip be recorded, the alarm sensor 10 can upload (S9) it to the central unit 14 automatically (from where it can be sent to the remote monitoring centre 20 either automatically or upon request), or the audio clip can be uploaded to the central unit 14 only if there is a specific command or request (S10) (sent from the central unit 14 or by an operator in the remote monitoring centre 20 where alarms of alarm installations are monitored). A user can, in some embodiments, replay the audio clip (either at the central unit 14 directly or remotely via a mobile device) to obtain additional context on the event which triggered the recording of the audio clip and the associated alarm.

[0060] The audio clip can be analysed in the remote monitoring centre 20 by an operator so that additional context on the alarm is made available to the personnel there, to help verify a true alarm or to help cancel or de-escalate a false alarm.

[0061] In some embodiments, an audio clip is recorded by the alarm sensor 10 which has detected a trigger. In other embodiments of the invention, a recording command signal (S2; S3) is sent to an alarm sensor 10 which has not (e.g. not yet) detected a trigger, by either the central unit 14 or the remote monitoring centre 20. A recording command signal (S2) can be sent from the central unit 14 automatically in response to some other trigger occurring at the premises and processed by the central unit 14. In addition or alternatively, a recording command signal (S3) can be sent from an operator at the remote monitoring centre 20 in order to make available additional context information.

[0062] As an example, an alarm installation is considered which comprises in the building several audio-equipped window / door alarm sensors 10, and perhaps other sensors (PIR motion detectors, or PIR-cameras). In response to an initial alarm trigger somewhere in the alarm installation, transmitted via the installation’s central unit 14 to the remote monitoring centre 20, either the central unit 14 (automatically) or the operator at the remote monitoring centre 20 (acting via the central unit 14) may generate a recording command signal (S2; S3) to command all of the window / door alarm sensors to record an audio clip, even if the individual alarm sensors have not been triggered locally.

[0063] This gives the operator at the remote monitoring centre 20 access to audio from several different sources, to provide additional context information.

[0064] According to one possible embodiment, the audio clip or more precisely the audio signal is classified (S11 ; S12) by a classification device. Classification can be performed by a classification device incorporated into the microcontroller 30, incorporated into the central unit 14, or provided at the remote monitoring centre 20. The classification device may be implemented by software running on a processor of the sensor 10, or of the central unit 14, or at the monitoring centre. Classification (S11 ; S12) is performed by a pre-trained machine-learning algorithm. As an example, input data is classified by a machine-learning model comprising a convolutional neural network (CNN) to produce a classification result, wherein the input data is based at least in part on an audio signal provided by the microphone 36 of the alarm sensor 10. The classification result indicates a correspondence of the input data with alarm installation related events such as glass-break, door-break, window-break, dog barking, humans, speaking, shouting, and screaming. For example, the machine-learning algorithm may at least be trained with a plurality of audio signals or audio clips corresponding to different situations, i.e., events, related to an alarm installation; the training preferably includes an indication of the situations corresponding to some or all audio signals or audio clips used in the training so as to associate audio (e.g., features in the audio signals or audio clips) with the situations. By way of example, audio signals or audio clips of situations like, e.g., glass-break, dog barking, shouting, etc.

[0065] Classification result data is generated based on the classification. The classification result data can be a code word which indicates the nature of the identified incident which was recorded in the audio clip (e.g. a code word indicating “glass breaking”).

[0066] If classification (S11) is performed by the alarm sensor 10, an embodiment of the invention provides that in a first step, not the entire audio clip is sent from the alarm sensor 10 to the central unit 14 but only the classification result data. This saves battery life as sending the classification result data requires less energy than sending the entire audio clip. Further, in view of the limited bandwidth of the transmission between the alarm sensor 10 and the central unit 14, sending classification result data is faster than sending an entire audio clip. Classification result data may be transmitted automatically, or it may be transmitted in response to an upload command (S10).

[0067] Should a user of the alarm installation or personnel in the remote monitoring centre want to listen to the entire audio clip, an upload request (S10) is sent to the alarm sensor, and the entire audio clip is sent to the central unit 14 from where it can be sent to the remote monitoring centre 20.

[0068] An advantage of making available to the personnel in the remote monitoring centre 20 the classification result data is that a decision on the nature of the alarm can be taken faster as compared to a scenario in which a couple of audio clips are being sent which an operator in the remote monitoring station 20 has to listen to, possibly a few times until he / she understands what sound has been recorded. Instead, the operator can either take a decision immediately based on the classification result data (indicating e.g. “glass breaking”) or replay only the audio clip which appears to be, based on the classification result data, the most relevant one.

[0069] The audio clip is preferably deleted at some point (S13), both with a view to memory constraints in the alarm sensor 10 and with a view to data privacy. Like camera images, audio is subject to data privacy considerations. This is potentially even more relevant than camera images as audio capture may be less directional compared to a camera. For example, if a window or door is open, it may record audio from outside the premises.

[0070] Deletion (S13) can be done in response to reception at the sensor 10 of a deletion command signal (S14) or automatically after a predefined time period has lapsed.

[0071] A deletion command signal (S14) can be sent from the remote monitoring centre 20 or the control unit 14 after an alarm situation has been cleared.

[0072] Should an audio clip have been recorded without there being a subsequent upload request from the control unit 14 or the remote monitoring centre 20, the audio clip can be automatically deleted (S14) when enough time has lapsed so that it is clear that the audio clip will no longer be used. Examples of such time periods are 24 hours, 12 hours, or 1-2 hours, 30 minutes, 20 minutes, 10 minutes, or less.

[0073] In an embodiment of the invention, the audio clip is automatically deleted after a predetermined time has lapsed, and also in a situation in which the audio clip has been uploaded to the central unit 14. Such automatic-delete ensures, with a view to data privacy, that the audio clip is deleted even if there is no explicit deletion command signal.

[0074] The clip might be over-written anyway by a subsequent audio clip recording, but using explicit automatic-deletion would ensure that no clip is retained on-device for longer than is justifiable. Deletion of an audio clip can be performed by actual erasure, by over-writing with other data, or by erasing a pointer to the recording in memory, or by destroying an access or encryption key to the recording.

[0075] In the foregoing example, communication with the alarm sensor 10 is generally via the central unit 14. For example, in Figure 3, communications to and from the remote monitoring centre 20 generally pass via the central unit 14. However, as mentioned above, in some embodiments, the central unit 14 of the installation may be omitted. In such case, where the functionality of the central unit 14 is not implemented at the installation itself (e.g. in another sensor, camera, keypad, doorbell, etc), the sensors 10 may communicate independently with the remote monitoring centre. Communications to and from the central unit 14, described above, will then be understood to be with the remote monitoring centre 20. In Figure 3, the functionalities represented in the central unit 14 would be merged into the functionalities at the remote monitoring centre 20.

Claims

Claims1 . An alarm sensor for a window or a door, comprising a magnetic detector, a shock and / or movement detector, and a microphone, wherein the alarm sensor is configured to process signals from the magnetic detector and from the shock and / or movement detector to detect an event of opening and / or breach of the door or window, wherein the alarm sensor is configured to generate an event detection trigger signal at least based on the processed signals, and wherein the alarm sensor is configured to process, following the generated event detection trigger signal, a signal from the microphone to provide contextual information regarding the detected event.

2. The alarm sensor of claim 1 , wherein the alarm sensor is configured to cause activation of the microphone following the generated event detection trigger signal and / or the microphone is configured to get activated following the generated event detection trigger signal.

3. The alarm sensor of any one of the preceding claims, wherein the alarm sensor is configured to transmit the contextual information.

4. The alarm sensor of any one of the preceding claims, wherein the contextual information is at least indicative of a type of event related to an alarm installation.

5. The alarm sensor of any one of the preceding claims, wherein processing of the signal from the microphone comprises classifying the signal with a pretrained machine-learning algorithm.

6. The alarm sensor of claim 5, wherein the pre-trained machine-learning algorithm is at least trained with a plurality of audio signals or audio clips corresponding to different events related to an alarm installation.

7. The alarm sensor of any one of the preceding claims, wherein the sensor comprises a tamper detector.

8. The alarm sensor of any one of the preceding claims, wherein the shock and / or movement detector comprises at least one of a piezo shock / vibration detector and an accelerometer.

9. The alarm sensor of any one of the preceding claims, wherein the sensor includes a receiver and a transmitter for communicating with another device, optionally with a central unit of an alarm installation.

10. The alarm sensor of any one of the preceding claims, wherein the sensor is configured to be surface mounted to a movable or fixed part of a door or window, optionally independently of a locking mechanism of the door or window.11 . A method of operating an alarm sensor according to any one of the preceding claims in an alarm installation, the alarm installation comprising a central unit, the method comprising the step of activating the microphone of the alarm sensor in response to a trigger signal.

12. The method of claim 11 , further comprising: processing signals from the magnetic detector and from the shock and / or movement detectorto detect an event of opening and / or breach of a door or a window; generating the trigger signal at least based on the processed signal; and processing, following the activation of the microphone, a signal from the microphone to provide contextual information regarding the detected event.

13. The method of claim 11 , further comprising the step of transmitting the contextual information to the alarm installation.

14. The method of any one of claims 11 to 13, wherein the trigger signal originates from at least one of the magnetic detector, the shock and / or movement detector, and a tamper detector of the alarm sensor.

15. The method of any one of claims 11 to 13, wherein the trigger signal originates from the central unit.

16. The method of any one of claims 11 to 15, wherein the installation has a disarmed state, and at least one armed state, wherein the trigger signal is generated only when the alarm installation is in an armed state.

17. The method of any one of claims 11 to 16, wherein the alarm installation comprises a transceiver for communicating via a data connection with a remote monitoring centre, wherein the method comprises the step of providing to the alarm sensor a trigger signal originating from the remote monitoring centre.

18. The method of any one of claims 11 to 17, wherein the contextual information at least indicative of a type of event related to an alarm installation.

19. The method of any one of claims 11 to 18, wherein an audio signal captured by the microphone is classified by a classification device, optionally within the alarm sensor or within the central unit.

20. The method of claim 19, wherein the classification device runs a pre-trained machine-learning algorithm for classifying the audio signal.

21. The method of claim 20, wherein the pre-trained machine-learning algorithm is at least trained with a plurality of audio signals or audio clips corresponding to different events related to an alarm installation.

22. The method of any one of claims 19 to 21 , wherein information on classification of the audio signal is sent to a remote monitoring centre and an entire audio clip corresponding to an audio signal captured by the microphone is sent to the remote monitoring centre upon receipt of a specific request from the remote monitoring centre.

23. The method of any one of claims 11 to 22, wherein an audio clip corresponding to an audio signal captured by the microphone is automatically deleted after a predefined time period has lapsed.

24. The method of any one of claims 11 to 23, wherein a deletion command signal for deletion of an audio clip is transmitted to the alarm sensor.

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