System comprising head-mounted device and hand-held device and configured to detect use of hand-held device by user wearing head-mounted device

Abstract

A system and computer-implemented method comprising a head-mounted device and a hand-held device and configured to detect use of the hand-held device by a user wearing the head-mounted device, the system comprising a head-mounted device and a hand-held device, the system configured to detect use of the hand-held device by a user wearing the head-mounted device. The system is further configured to determine a relative movement of one of the head-mounted device and the handheld device relative to the other of the head-mounted device and the handheld device, and to detect use of the handheld device by the user based on the relative movement.

Description

Technical Field

[0001] The present disclosure relates to a system, which includes a head-mounted device and a hand-held device and is configured to detect the use of the hand-held device by a user wearing the head-mounted device. The present disclosure also relates to a computer-implemented method configured for the system. Background Art

[0002] Detecting usage of a handheld device by a user wearing a head mounted device may be useful for implementing a number of actions, for example, to adapt values ​​of parameters of functionality of the handheld device and / or the head mounted device.

[0003] Some systems in the prior art can achieve this detection based on image sensors. However, these systems have several disadvantages. For example, the disadvantage of these systems is that they have poor performance in dim light conditions.

[0004] According to the present disclosure, the system allows for detection of use of a handheld device and avoids the previously described disadvantages. Summary of the invention

[0005] A simplified overview is presented below to provide a basic understanding of different aspects of the present disclosure. This overview is not an extensive review of all contemplated aspects, and is neither intended to point out the key or important elements of all aspects, nor to delineate the scope of any or all aspects. The sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to a more detailed description presented later.

[0006] One aspect of the present disclosure is a system. The system includes a head-mounted device and a handheld device. The system is configured to detect the use of the handheld device by a user wearing the head-mounted device. The system is also configured to determine the relative movement of one of the head-mounted device and the handheld device relative to the other of the head-mounted device and the handheld device, and detect the use of the handheld device by the user based on the relative movement.

[0007] The system of the present disclosure allows for faster determination of the user's use of the handheld device. Thanks to this faster determination, the values ​​of the parameters of the functions of the handheld device or head-mounted device can be adapted faster, and thus the user can use the handheld device more comfortably faster.

[0008] Another aspect of the present disclosure is a computer-implemented method for detecting use of a handheld device by a user wearing a head-mounted device. The computer-implemented method includes: determining a relative motion of one of the head-mounted device and the handheld device relative to the other of the head-mounted device and the handheld device; and detecting use of the handheld device by the user based on the relative motion.

[0009] The computer may include a memory and a processor. Examples of processors include microprocessors, microcontrollers, graphics processing units (GPUs), central processing units (CPUs), application processors, digital signal processors (DSPs), reduced instruction set computing (RISC) processors, systems on chip (SoCs), field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform various functions described throughout the present disclosure. The memory may be a computer-readable medium. As an example and not limitation, such a computer-readable medium may include a random access memory (RAM), a read-only memory (ROM), an electrically erasable programmable ROM (EEPROM), an optical disk storage device, a magnetic disk storage device, other magnetic storage devices, a combination of computer-readable media of the above type, or any other medium that may be used to store instructions or data structures that a processor of a computer can access.

[0010] Another aspect of the present disclosure is a computer-readable non-transitory program storage device tangibly embodying a program of instructions executable by a computer to perform a computer-implemented method for detecting use of a handheld device by a user wearing a head-mounted device. The computer-implemented method includes: determining a relative motion of one of the head-mounted device and the handheld device relative to the other of the head-mounted device and the handheld device; and detecting use of the handheld device by the user based on the relative motion. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] For a more complete understanding of the description provided herein and the advantages thereof, reference is now made to the following brief description taken in conjunction with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.

[0012] Figure 1 Represents a system that includes both handheld devices and head-mounted devices.

[0013] Figure 2 An example of feature points representing a user's face.

[0014] Figure 3 An example of a 3D model representing a face.

[0015] Figure 4 Represents 3 coordinate systems.

[0016] Figure 5 Represents the feature points of the iris.

[0017] Figure 6 Represents the distance between the two pupils and the distance between the user's eyes and the handheld device.

[0018] Figure 7A first example of a method for detecting use of a handheld device by a user wearing a head mounted device is shown.

[0019] Figure 8 A second example of a method for detecting use of a handheld device by a user wearing a head mounted device is shown.

[0020] Fig. 9 A second example of a method for detecting use of a handheld device by a user wearing a head mounted device is shown. DETAILED DESCRIPTION

[0021] The detailed description set forth below in conjunction with the accompanying drawings is intended as a description of different possible embodiments, rather than being intended to represent the only embodiments that can implement the concepts described herein. For the purpose of providing a thorough understanding of the different concepts, the detailed description includes specific details. However, it is clear to those skilled in the art that these concepts can be implemented without these specific details. In some cases, well-known structures and components are shown in block diagram form to avoid obscuring these concepts.

[0022] Description of a system including a handheld device and a head mounted device

[0023] Figure 1 A system 101 including a handheld device 102 and a head mounted device 103 is shown.

[0024] The system 101 may include a detection module configured to detect use of the handheld device 102 by a user wearing the head mounted device 103 .

[0025] The detection module may include at least one processor and at least one memory. The at least one processor and at least one memory may be configured to implement a method for detecting the use of the handheld device 102 by a user wearing the head mounted device 103 .

[0026] The detection module may be integrated into the handheld device 102 or the head mounted device 103 .

[0027] Examples of processors include microprocessors, microcontrollers, graphics processing units (GPUs), central processing units (CPUs), application processors, digital signal processors (DSPs), reduced instruction set computing (RISC) processors, systems on a chip (SoCs), baseband processors, field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functions described throughout this disclosure.

[0028] The memory may be a computer-readable medium. By way of example and not limitation, such a computer-readable medium may include a random access memory (RAM), a read-only memory (ROM), an electrically erasable programmable ROM (EEPROM), an optical disk storage device, a magnetic disk storage device, other magnetic storage devices, a combination of the above types of computer-readable media, or any other medium that can be used to store computer-executable code in the form of instructions or data structures that can be accessed by a processor of a computing module.

[0029] When the detection module is integrated into the handheld device 102, the detection module may be integrated into a system on chip (SoC) of the handheld device 102. The system on chip may also be configured to implement other functions of the handheld device 102.

[0030] When the detection module is integrated into the head mounted device 103, the detection module may be integrated into a system on chip (SoC) of the head mounted device 103. The system on chip may also be configured to implement other functions of the head mounted device 103.

[0031] The handheld device 102 may be an electronic device, such as a device including an electronic display. The electronic device may be a smartphone, a computer, or a tablet computer.

[0032] The head mounted device 103 may be glasses (eg, smart glasses) or a clip configured to be attachable to glasses.

[0033] The head mounted device 103 may further include an optical device, which may be an active optical device.

[0034] The active optical device may be an electrochromic optical lens or may be configured as a display element. For display elements, the active optical element may include a light-guiding optical element (LOE).

[0035] An active optical device refers to an optical device in which the value of a parameter of a function of the optical device can be modified as desired. The value of the parameter can be modified by applying a signal (e.g., an electrical signal) to a terminal of the active optical device. The function can be one of the following:

[0036] · Transmittance levels of active optical devices,

[0037] · Tone of active optical devices,

[0038] The reflectivity level of active optical devices, and

[0039] Polarization parameters of active optical devices, such as the polarization angle of the active optical device,

[0040] The optical power of the active optical device,

[0041] Elements displayed by the active optical device. These elements may be images, symbols, letters or text. In an embodiment, the elements to be displayed and the positions of these elements may be selected.

[0042] The handheld device 102 may include a motion determination module.

[0043] The head mounted device 103 may include a motion determination module.

[0044] The motion determination module of the handheld device 102 may be an inertial measurement unit (IMU).

[0045] The motion determination module of the head mounted device 103 may be an inertial measurement unit (IMU).

[0046] The handheld device 102 may include an eye tracking module.

[0047] The head mounted device 103 may include an eye tracking module.

[0048] The handheld device 102 may include a distance module.

[0049] The head mounted device 103 may include a distance module.

[0050] The eye tracking module and the distance module of the handheld device 102 or the head mounted device 103 may be true depth sensors.

[0051] The distance module may be configured to determine the distance between the handheld device 102 and the head mounted device 103 or the user's eyes.

[0052] The system 101 of the present disclosure allows for detection of a user's use of a handheld device 102. Once use is detected, the system 101 can be configured to adapt the values ​​of parameters of the functions of the handheld device 102 or the head mounted device 103. The purpose of such adaptation is to allow for better use of the handheld device 102.

[0053] Adaptation of these values ​​and quick detection of use of the handheld device 102 allows for more comfortable use of the handheld device 102 .

[0054] The handheld device 102 and / or the head mounted device 103 may include a camera.

[0055] Images of the user's face may be obtained using a camera of the handheld device 102. These images may be used to determine usage of the handheld device 102, for example, by determining the user's gaze axis.

[0056] The images of the user's face may be processed independently frame by frame. The images may be processed in real time. The camera of the handheld device 102 may be enabled in the background while the handheld device 102 is held by the user.

[0057] In order to determine the angle of the user's head, the positions of the feature points of the user's face on the image acquired by the camera may be extracted. These feature points may be selected from the following:

[0058] - the left corner of the left or right eye,

[0059] - the right corner of the left or right eye,

[0060] -tip of the nose,

[0061] -Left corner of mouth,

[0062] -Right corner of mouth, and

[0063] -jaw.

[0064] Figure 2 An example of this feature point 201 is shown.

[0065] use Figure 2 The feature points 201 can determine the 3D model of the user's face. Figure 3 An example of a 3D model of a face in which feature points 201 are located is shown.

[0066] You can get the parameter values ​​of the camera parameters. These values ​​can be represented as the following 3x 3 matrix, which can be used during the determination of the head pose:

[0067]

[0068] f x and f y is the focal length of the camera, and c x and c y is the value of the optical center of the camera. Although camera parameters may be unique to a particular camera, they can be estimated from the image (the image presented on the image plane). x and f y Both can be proportional to the width of the image, and the coordinates at the middle width and middle height of the image can be assumed to be the optical center of the camera.

[0069] After obtaining the required parameters, the angles of the head can be determined. There are three coordinate systems that can be used to determine these angles. These coordinate systems are Figure 4401 is a world coordinate, where the coordinates are U, V, and W. 402 is an image plane coordinate, where the coordinates are x and y. 403 is a camera coordinate, where the coordinates are X, Y, and Z. The image plane coordinate 402 may be a screen of the handheld device 102. The coordinates of the feature points 201 of the face in the world coordinate 401 may be determined based on the coordinates in the camera coordinate 403 using, for example, a transformation including a rotation R and a translation t. The feature points 201 in the camera coordinate 403 may be projected in the image plane coordinate 402 using the intrinsic parameters of the camera (focal length, optical center, etc.).

[0070] The relationship between image coordinates and camera coordinates based on the camera's intrinsic parameters can be modeled using the following equation:

[0071]

[0072] Here, the camera coordinates may be transformed into world coordinates through translation and rotation transformations (ie, head angle and translation).

[0073]

[0074] The images obtained from the camera of the handheld device 102 can also be used to determine the movement of the user's iris. The skilled person will know how to achieve this determination, for example, the skilled person will know how to use an iris tracking model to obtain the landmarks of the iris. The skilled person can use the mediapipe library of Google. Five feature points of the iris can be determined (4 feature points on the circumference of the iris and 1 feature point at the center of the iris). The coordinates of the center of the iris are extracted to track the frame-to-frame movement of the iris. Figure 5 A feature point 501 represents an iris.

[0075] Using the images obtained from the camera of the handheld device 102, the distance between the handheld device 102 and the user's eyes may also be determined.

[0076] This distance can be estimated using a scaled reference method. The distance between the user's two pupils and the corresponding value of the number of pixels in the image may be required. Figure 6 represents the distance P' between the two pupils and the distance D' between the user's eyes and the handheld device 102. The distance D' can be obtained using the following formula:

[0077] D′=F*pd / P′

[0078] Where F is the focal length (in pixels), pd is the distance between the two pupils (in cm), and P' is the distance between the two pupils in the image (in pixels).

[0079] Images of the user's field of view may be obtained using a camera of the head mounted device 103. These images may be used to determine the use of the handheld device 102, for example, by determining when the handheld device 102 is within the user's field of view.

[0080] Description of a method for detecting use of a handheld device by a user wearing a head mounted device

[0081] Figure 7 Schematically shows a method for detecting the use of the handheld device 102 by a user wearing the head mounted device 103. The method for detecting the use of the handheld device 102 by a user wearing the head mounted device 103 includes:

[0082] - a step 701 of determining a relative movement of one of the head mounted device 103 and the hand held device 102 relative to the other of the head mounted device 103 and the hand held device 102,

[0083] - A step 702 of detecting usage of the handheld device 102 by the user based on the relative movement.

[0084] The relative motion of a first object with respect to a second object refers to the motion of the first object in a reference frame in which the second object is fixed.

[0085] The relative motion may be determined based on the absolute motion of the handheld device 102 and the absolute motion of the head mounted device 103 .

[0086] The absolute motion of the handheld device 102 may be obtained from the motion determination module of the handheld device 102 .

[0087] The absolute motion of the head mounted device 103 may be obtained from a motion determination module of the head mounted device 103 .

[0088] In an embodiment, the step 702 of detecting the user's use of the handheld device 102 may include:

[0089] - determine the values ​​of the parameters of the relative motion,

[0090] -Determining when the user is using the handheld device by comparing the value to a predetermined threshold.

[0091] The parameter of the relative movement may be the speed of the relative movement, for example expressed in ° / s. According to tests carried out by the applicant, the predetermined threshold may be selected between 10° / s and 6° / s.

[0092] The parameter may be the amplitude of the relative motion, or a change in the relative motion (eg a first or second derivative of the amplitude of the relative motion).

[0093] The value may be compared to a predetermined threshold, and when the value is below the predetermined threshold, the user is considered to be using the electronic device.

[0094] like Figure 3 As presented in the examples, Figure 2 When it is detected that the user is using the handheld device 102 , the method may further include step 801 : adapting the value of the parameter of the function of the element of the handheld device 102 toward the optimal value.

[0095] The optimal value may be a value of a parameter of a function of an element of the handheld device 102 that makes the user most comfortable using the handheld device 102. For example, the handheld device 102 may be configured to display elements of a screen of the handheld device 102 so that the user holds the handheld device 102 at the Harmon distance. The Harmon distance is the most comfortable distance for close work. The Harmon distance is determined by the distance between the tip of the elbow and the middle of the index finger.

[0096] The higher the confidence in the detection that the user is using the handheld device 102 , the better the values ​​of the parameters of the functions of the elements of the handheld device 102 can be adapted towards optimal values.

[0097] For example, if the test of the previous section is used, the adaptation of the value towards the optimal value is increased as the predetermined threshold decreases.

[0098] In an embodiment, Figure 7 or Figure 8 The method may further include the following steps when it is detected that the user is using the handheld device 102: adjusting the value of the parameter of the function of the element of the head mounted device 103 towards the optimal value.

[0099] As described above, the optimal value may be a value of a parameter of a function of an element of the head mounted device 103 that makes the user most comfortable using the handheld device 102 .

[0100] The element of the head mounted device 103 may be an optical device or an active optical device. When the element is an active optical device, the function may be selected from the functions described above.

[0101] The higher the confidence in the detection of the user using the handheld device 102 , the more the values ​​of the parameters of the functions of the elements of the head mounted device 103 can be adapted towards the optimal values ​​of the parameters of the functions of the elements of the head mounted device 103 .

[0102] For example, if the test of the previous section is used, the adaptation of the value towards the optimal value is increased as the predetermined threshold decreases.

[0103] Optimal values ​​for the functionality of an element of the head mounted device 103 or optimal values ​​for the functionality of an element of the head mounted device 103 may depend on values ​​of environmental parameters and / or values ​​of physiological parameters of the user.

[0104] Environmental parameters can include:

[0105] - Instructions for enabling Wi-Fi,

[0106] - a certain amount of ambient light,

[0107] - the distance between the user's eyes and the handheld device 102,

[0108] - the type of handheld device 102,

[0109] - the type of use the user makes of the handheld device 102 (e.g., reading, scrolling through pictures or articles, or watching a movie) and / or

[0110] - Indoor or outdoor conditions.

[0111] The user's physiological parameters may include:

[0112] - User's age

[0113] - the user's refraction, and / or

[0114] - Parameters representing the user's visual performance, such as the user's visual acuity and the user's dynamic visual acuity.

[0115] Fig. 9 express Figure 7 Another embodiment of the method. Fig. 9 As presented in , the step 701 of determining the relative motion and the step 702 of detecting the use of the handheld device 102 based on the relative motion may form a first test 901. Fig. 9 As presented in , the method of the present disclosure may also include step 902 of using a second test to detect the user's use of the handheld device 102. Fig. 9 As presented in , the method of the present disclosure may further include step 903 of implementing a second adaptation of the value of the parameter of the function of the element of the handheld device 102 when the second test 902 is used to detect that the user is using the handheld device 102 .

[0116] The first adaptation may depend on the value of a parameter of the first test 901 , and / or the second adaptation may depend on the value of a parameter of the second test 902 .

[0117] The first test 901 and the second test 902 may be implemented in an order in which the confidence level of the first test 901 and the confidence level of the second test 902 increase.

[0118] This classification usually means that the tests are actually sorted in order of increasing complexity.

[0119] In an embodiment, when the confidence level of the first test 901 is higher than the confidence level of the second test 902, the value of the function of the element of the handheld device 102 can be adapted toward the optimal value more during the first adaptation than during the second adaptation. When the confidence level of the first test 901 is lower than the confidence level of the second test 902, the value of the function of the element of the handheld device 102 can be adapted toward the optimal value more during the second adaptation than during the first adaptation.

[0120] In an embodiment, during the second adaptation, the value of the functionality of the element of the head mounted device 103 is adapted in addition to or instead of the value of the functionality of the element of the handheld device 102 .

[0121] In an embodiment, when the confidence level of the first test 901 is higher than the confidence level of the second test 902, the value of the function of the element of the head mounted device 103 can be adapted toward the optimal value more during the first adaptation than during the second adaptation. When the confidence level of the first test 901 is lower than the confidence level of the second test 902, the value of the function of the element of the head mounted device 103 can be adapted toward the optimal value more during the second adaptation than during the first adaptation.

[0122] The second test 902 may include detecting a gaze axis of the user, and when the detected gaze axis passes through the handheld device 102 , use of the handheld device 102 is detected.

[0123] Detection of the user's gaze axis may be achieved using an eye tracking module of handheld device 102 or using an eye tracking module of head mounted device 103 .

[0124] The second test 902 may include determining the distance between the head mounted device 103 and the handheld device 102. When the distance is below a distance threshold, use of the handheld device 102 is detected.

[0125] The second test 902 may include detecting receipt of a notification by the handheld device 102, where use of the handheld device is detected when the handheld device 102 receives the notification.

[0126] The second test 902 may include determining whether the screen of the handheld device 102 is turned on, and when the screen of the handheld device 102 is determined to be turned on, use of the handheld device is detected.

[0127] The second test 902 may include obtaining signals from sensors of the handheld device 102 and the head mounted device 103 and inputting these signals into a machine learning module to determine whether the user is using the handheld device 102. The machine learning module may have been previously trained with model signals associated with an indication of whether the user is using the handheld device 102, respectively.

[0128] The second test 902 may include obtaining a signal from an IMU of the handheld device 102 or an IMU of the head mounted device 103 to determine the angle of the user's head, for example, using a camera of the head mounted device 103 or the handheld device 102 and the distance between the handheld device 102 and the head mounted device 103 or the user's face. Based on the signal, angle, and distance, the user's use of the handheld device 102 may be detected.

[0129] In an embodiment, a third test, a fourth test, etc. associated with the third adaptation and the fourth adaptation may be implemented.

[0130] Description of use cases of the disclosed methods and systems

[0131] In a use case, the head mounted device 102 may be smart glasses having at least one sensor for measuring the movement of the user's head, active lenses (e.g., electrochromic optical lenses or active lenses on which the power of the lenses can be adapted), a camera, and an inertial module unit. The handheld device intended for use by the user may be a smartphone. The smartphone may include a camera and an inertial module unit.

[0132] In a first test, images obtained by a smartphone's camera may be used to detect a user's use of the smartphone.

[0133] In a second test, images obtained by the camera of the smart glasses can be used to detect the user's use of a smartphone. To achieve detection, an estimation of the user's field of view can be achieved based on the images and determining whether the smartphone is in the field of view.

[0134] In a third test, the IMU of the smartphone and / or the IMU of the smart glasses can be used to detect the movement of the user's head. For example, the signal from the IMU of the smartphone and / or the IMU of the smart glasses can be input into a machine learning model.

[0135] In a fourth test, it is detected that the smartphone receives the notification, and in this case, it can be considered that the user is using the smartphone.

[0136] Based on the four tests presented above, once the use of a smartphone is detected, the values ​​of environmental parameters can be obtained (indication of whether Wi-Fi is enabled, indication of whether the user is indoors or outdoors, the user's positioning, the distance between the user's eyes and the smartphone, the type of smartphone, the type of use of the smartphone by the user).

[0137] Based on the values ​​of these environmental parameters and possibly the values ​​of physiological parameters (for example and advantageously the user's refraction), the values ​​of the functions of the active lenses can be adapted as soon as the use of a smartphone is detected.

Claims

1. A system (101), comprising a head mounted device (103) and a hand held device (102), wherein the system (101) is configured to detect use of the hand held device (102) by a user wearing the head mounted device (103), The system (101) is also configured to: - determining a relative motion of one of the head mounted device (103) and the hand held device (102) relative to the other of the head mounted device (103) and the hand held device (102), and - detecting usage of the handheld device (102) by the user based on the relative movement.

2. The system (101) according to claim 1, The head mounted device (103) comprises a motion determination module, and / or The handheld device (102) includes a motion determination module.

3. The system (101) according to claim 1 or 2, The system (101) is also configured to: - determining the value of a parameter of said relative movement, - determining when the user is using the handheld device (102) by comparing the value to a predetermined threshold.

4. The system (101) according to any one of claims 1 to 3, The system (101) is also configured to: - when it is detected that the user is using the handheld device (102), the value of the parameter of the function of the element of the head mounted device (103) is adapted towards the optimal value.

5. The system (101) according to claim 4, the optimal value being dependent on a value of an environmental parameter and / or a value of a physiological parameter of the user.

6. The system (101) according to claim 4 or 5, Determining the relative movement and detecting the use of the handheld device (102) by the user based on the relative movement together constitute a first test (901), The adaptation is a first adaptation, The system (101) is configured to: - using a second test (902) to detect usage of the handheld device (102) by the user, - when using the second test (902) it is detected that the user is using the handheld device (102), a second adaptation of the value of the parameter of the function of the element of the head mounted device (103) towards the optimal value is performed.

7. The system (101) according to claim 6, The first adaptation depends on the value of a parameter of the first test (901), and / or The second adaptation depends on the value of a parameter of the second test (902).

8. The system (101) according to claim 6 or 7, The system is configured to implement the first test (901) and the second test (902) in an order of increasing confidence level of the first test (901) and confidence level of the second test (902).

9. The system (101) according to claim 8, The system (101) is configured to: - when the confidence level of the first test (901) is higher than the confidence level of the second test (902), the value of the function of the element of the head mounted device (103) is adapted towards the optimal value more during the first adaptation than during the second adaptation, and / or - When the confidence level of the first test (901) is lower than the confidence level of the second test (902), the value of the function of the element of the head mounted device (103) is adapted towards the optimal value during the second adaptation period more than during the first adaptation period.

10. The system (101) according to any one of claims 6 to 9, The second test (902) includes detecting a gaze axis of the user, and detecting use of the handheld device (102) when the detected gaze axis passes through the handheld device.

11. The system (101) according to any one of claims 6 to 9, The second test (902) includes detecting receipt of a notification by the handheld device (102), detecting use of the handheld device (102) when the handheld device (102) receives the notification, and / or The second test (902) includes determining whether a screen of the handheld device (102) is turned on, and when the screen of the handheld device (102) is determined to be turned on, use of the handheld device (102) is detected.

12. The system (101) according to any one of claims 4 to 11, The optimal value is a first optimal value, The system (101) is also configured to: - when it is detected that the user is using the handheld device (102), adapting the value of a parameter of a function of an element of the handheld device (102) towards a second optimal value.

13. The system (101) according to any one of claims 1 to 12, The head mounted device (103) is glasses or a clip configured to be attachable to glasses.

14. The system (101) according to any one of claims 1 to 13, The handheld device (102) is a smart phone.

15. A computer-implemented method for detecting use of a handheld device by a user wearing a head mounted device, The computer-implemented method comprises: - determining (701) a relative motion of one of the head mounted device and the hand held device relative to the other of the head mounted device and the hand held device, - Detecting (702) usage of the handheld device by the user based on the relative movement.

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