Abstract:
The present disclosure provides a method of operating a wearable life logging device ( 2 ) comprising a data processing unit ( 9 ), a camera unit ( 7 ), and at least one motion sensor ( 4, 5 ). The method comprises selectively operating the device in a take photo state ( 200 ), wherein a photo is captured by means of the camera unit ( 7 ), and selectively operating the device in a sleep state ( 300 ), wherein the camera unit ( 7 ) is in a low power mode. The method further comprises causing the device to transition ( 120,   330, 430 ) to the take photo state ( 200 ) in response to a signal from the motion sensor ( 4, 5 ).

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to a method for lifelogging and to a system which implements such a method. 
       BACKGROUND 
       [0002]    Lifelogging is the process of digitally lifelogging life experiences. A lifelogging system usually comprises a wearable lifelogging device which automatically and continuously captures the user&#39;s activities in the form of text and/or sensor data, such as image, audio or video lifeloggings which are stored and organized for future use. 
         [0003]    People may want to log their activities for their own enjoyment, for example for keeping a diary or being able to retrieve and share personal experiences, including unanticipated ones, with others. Lifelogging may also be used for medical purposes, for example as an aid for people suffering from memory impairment. 
         [0004]    Another application for lifelogging devices is one of personal security; a lifelogging device may be used to provide evidence in the event the user is harassed or attacked. 
         [0005]    Yet another application is one of quality assurance; a lifelogging device may be used to document the user&#39;s activity. For example a police officer, nurse, physician, fireman, corrections officer, keeper or caretaker may use a lifelogging device to provide documentation of work performed and/or as evidence against accusations of malpractice or abuse. 
         [0006]    For a lifelog not to be inconvenient and cumbersome to produce, it is important that the lifelogging system be user friendly and interfere as little as possible with the user&#39;s daily routine. It is desirable to improve existing lifelogging systems in these respects. 
         [0007]    On the other hand, there remains a need to interact with the lifelogging system, e.g. in order to prevent it from taking photos in situations when this would be inappropriate or forbidden. 
         [0008]    There is also a need to manage battery capacity of the lifelogging device such that it will have the capability of taking photos for a sufficient period of time before it needs charging. 
       SUMMARY 
       [0009]    It is an objective to improve the user experience of lifelogging systems. A particular object is to provide a lifelogging system which is easy, efficient and satisfying to use. 
         [0010]    The invention is defined by the independent claims. Embodiments are set forth in the dependent claims and in the descriptions and drawings. 
         [0011]    According to a first aspect, there is provided a method of operating a wearable life logging device comprising a data processing unit, a camera unit and at least one motion sensor. The method comprises selectively operating the device in a take photo state, wherein a photo is captured by means of the camera unit, and selectively operating the device in a sleep state, wherein the camera unit is in a low power mode. The method further comprises causing the device to transition to the take photo state in response to a signal from the motion sensor. 
         [0012]    A lifelogging device is defined as a device which is configured for continuous or intermittent capture of images of the user and/or the user&#39;s experiences. Images thus captured may be associated with data indicating time/date and/or geographic position information for the respective image. The lifelogging device may be configured with an integrated intermediate image and data storage device. In the alternative, the lifelogging device may be configured for online transmission of image and data to a network-accessible storage device. 
         [0013]    The operating of the device in the take photo state may further comprise reading at least the motion sensor and optionally causing the device to transition from the low power mode. 
         [0014]    The method may further comprise causing the device to transition from the take photo state to the sleep state if the signal from the motion sensor is below a first threshold level or if a signal from the camera unit represents a light level lower than a predetermined second threshold value. 
         [0015]    The first threshold level may be set so as to indicate whether the device is stationary on a substantially flat surface or whether it is in motion. 
         [0016]    In one embodiment, the device may be caused to transition from the take photo state to the sleep state if the signal from the motion sensor has been below the first threshold value for a sufficient period of time or if the signal from the camera unit represents a light level lower than the first threshold value for a sufficient period of time. 
         [0017]    The periods of time may be same or different. 
         [0018]    The method may further comprise determining a gravity vector and causing the device to transition to the sleep state only if the gravity vector is within a predetermined range. 
         [0019]    In this context, the term “range” is to be understood as a range of directions. 
         [0020]    Hence, it is possible to determine the orientation of the device, and to condition the transition to the sleep state on the device having a specific orientation, such as horizontal. 
         [0021]    The term “horizontal” should be construed as horizontal +/−10°, +/−5° or +/−1°. 
         [0022]    In this manner, a user of the device is able to make the device transition to the sleep state by placing the device in a specific orientation, such as horizontal on a surface. Thereby, the device is, in a user friendly manner, prevented from taking photos in situations when it is not appropriate. Moreover, the user and others will recognize that, when the device is in the specific orientation, it will not take pictures. 
         [0023]    The method may further comprise selectively operating the device in a ready state, wherein the camera is active and wherein the data processing unit is in a low power mode. 
         [0024]    The method may further comprise causing the device to transition from the take photo state to the ready state if the signal from the motion sensor is above the first threshold value and/or if the signal from the camera unit represents a light level higher than the second threshold value. 
         [0025]    Optionally, the transition to the sleep state may require a lower second threshold value than a transition to the ready state. For example, it may be desirable to transition to sleep state only when there is substantially no light, while remaining in ready state when there is little light, although not sufficient to provide an acceptable photo. 
         [0026]    The device may be caused to transition from the ready state to the take photo state in response to a clock signal. 
         [0027]    The clock signal may be a real time clock signal provided by a device clock. 
         [0028]    The method may further comprise causing the device to transition from the ready state to the take photo state if the signal from the motion sensor represents a predetermined motion pattern, such as a particular sequence of motions. 
         [0029]    The predetermined motion pattern may be composed of one or more absolute values, which may occur within a predetermined time period. For example, two values exceeding a predetermined threshold value and received within a predetermined time interval may be understood as a “double tap”, i.e. the user taps the device twice with his/her finger in order to trigger it to take an ad hoc photo. 
         [0030]    The method as claimed in any one of the preceding claims, further comprising selectively operating the device in a snooze state, wherein the device checks at least one transition indicator. 
         [0031]    Such a transition indicator may be an indicator indicating that a particular event has occurred, such as the device having been shaken or received a clock signal. 
         [0032]    The method may further comprise causing the device to transition from the snooze state to the sleep state if the signal from the motion sensor is below a first threshold level or if the signal from the camera unit represents a light level lower than a predetermined second threshold value. 
         [0033]    The first threshold level may be set so as to indicate whether the device is stationary on a substantially flat surface or whether it is in motion. 
         [0034]    In the method, the device may be caused to transition from the snooze state to the sleep state if the signal from the motion sensor has been below the first threshold value for a sufficient period of time or if the signal from the camera unit represents a light level lower than the first threshold value for a sufficient period of time. 
         [0035]    The periods of time may be same or different. 
         [0036]    The method may further comprise determining a gravity vector and causing the device to transition to the sleep state only if the gravity vector is within a predetermined range. 
         [0037]    Hence, it is possible to determine the orientation of the device, and to condition the transition to the sleep state on the device having a specific orientation, such as horizontal. 
         [0038]    The method may further comprise causing the device to transition from the snooze state to the take photo state if the signal from the motion sensor exceeds the first threshold value and/or if the signal from the camera unit represents a light level higher than the second threshold value. 
         [0039]    The method may further comprise causing the device to transition from the sleep state to the snooze state if the signal from the motion sensor represents an absolute value larger than a third threshold level. 
         [0040]    For example, this third threshold value could be set such that it will indicate that the device is in motion, or it may be slightly higher, such that it will indicate that the device is being shaken, i.e. that the user deliberately shakes it to cause it to “wake up”. 
         [0041]    The method may further comprise increasing the third threshold level if a signal from the camera unit represents a light level higher than the predetermined second threshold level. 
         [0042]    Hence, it is possible to cause the camera to increase its tolerance for movements when it is too dark to take acceptable photos. 
         [0043]    The method may further comprise causing the device to transition from the sleep state to the snooze state in response to a clock signal. 
         [0044]    The method may further comprise causing the device to transition from the ready state to the take photo state if the signal from the motion sensor represents a predetermined motion pattern, such as a particular sequence of motions. 
         [0045]    The method may further comprise causing the device to transition from the sleep state to the take photo state if the signal from the motion sensor represents a predetermined motion pattern, such as a particular sequence of motions, and/or if the signal from the motion sensor exceeds a first threshold value. Hence, the device may be caused to wake up to immediately take a photo upon recording a predetermined motion pattern and/or a sufficiently large/fast motion. 
         [0046]    The predetermined motion pattern may be composed of one or more absolute values, which may occur within a predetermined time period. For example, two values exceeding a predetermined threshold value and received within a predetermined time interval may be understood as a “double tap”, i.e. the user taps the device twice with his/her finger in order to trigger it to take an ad hoc photo. 
         [0047]    The method may further comprise that control parameters for the device is set by using a communication device having a first interface for communicating with the lifelogging device and a second interface for communicating with a network-based storage service. 
         [0048]    Thereby, the user may determine settings for the lifelogging device by using a communication device such as a Smartphone, a tablet computer, a desktop computer, a laptop computer etc which is able to control settings of the lifelogging device. For example, the rate at which photos are taken can be adjusted. Hence, a better user experience and a higher user friendliness is achieved. 
         [0049]    The method may further comprise sending a captured photo from the device to a storage device or a storage service via at least one wireless communication interface. The wireless interface may, as non-limiting examples, be a Bluetooth® interface or a WiFi interface to which the lifelogging device is connected. Another interface may be a wired interface, such as an electronic or optical fiber based interface, or a wireless interface, such as a cellular phone/data based interface. 
         [0050]    The photo taken by the lifelogging device may be a single photo, a sequence of photos or a video sequence. 
         [0051]    According to a second aspect, there is provided a wearable lifelogging device comprising a data processing unit, a camera unit, and at least one motion sensor. The device is configured to perform the method described above. 
         [0052]    The lifelogging device may have a front face (i.e. the face with camera lens) which is designed such that when placing the device face down on a horizontal surface, the amount of light reaching the camera lens will be sufficiently low for the camera to detect a light level lower than the first threshold value. For example, the camera may have a substantially planar front surface, with the camera lens being flush with, or retracted from, the front surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0053]      FIG. 1  is a schematic illustration of components of a lifelogging system.  FIGS. 2 a -2 c    are schematic illustrations of different configurations of a lifelogging system. 
           [0054]      FIG. 3  is a state diagram, which schematically illustrates operation of the lifelogging device  2 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0055]      FIG. 1  illustrates schematically components of a lifelogging system  1 . The system  1  comprises a wearable lifelogging device  2  which has a weather protected housing  3  which encloses a GPS unit  4 , an accelerometer  5 , a timer  6  (which may have the form of a real-time clock (RTC)), a camera  7 , a storage device  8  which may comprise volatile and non-volatile memory, a CPU  9 , a rechargeable battery  10 , a communication interface  11  and a user interface  12 . A clip  13  is arranged on the outside of the housing. The system  1  also comprises a first communication device  20  which has interfaces  21  and  22  for communicating with the lifelogging device  2  and a network-based storage service  30 , respectively. The first communication device  20  can have a controller  23  and a charger  24 . The network-based storage service  30  may comprise a storage service  31  and a computing service  32 . The network-based storage service  30  may also be connected to a second communication device  40  via the latter&#39;s interface  41 . The second communication device  40  also comprises application software  42 . 
         [0056]    Dashed lines represent connections  50 ,  51  and  52  between the components of the lifelogging system  1 . 
         [0057]    When a user wears the lifelogging device  2 , for example by attaching it to a piece of clothing or a necklace, the camera  7  may be preset to automatically take two photographs a minute. It is also possible to allow the user to trigger the camera to take a photograph by performing a predetermined gesture, such as tapping the camera once, twice or three times within a predetermined time period and possibly in a predetermined direction. 
         [0058]    When the lifelogging device takes a photo it may be a single photograph, a sequence of photos or a video sequence. A video sequence normally means a frame rate of more than 20 frames per second, whereas a sequence of photos may have a frame rate between 1 and 20 frames per second. A single photo refers to photos with a frame rate less than 1 frame per second, preferably on the order of one frame every 5-240 seconds, more preferably on the order of one frame every 20-120 seconds. 
         [0059]    The CPU  9  may be programmed to stop taking photographs, power off and/or cause the camera  7  to hibernate or go into a low-power mode (e.g. by turning off one or more other sensors), if it receives a predetermined sensor signal from the camera indicating that the photograph is darker than a predetermined level. 
         [0060]    The CPU  9  may also be programmed to stop taking photographs, power off and/or cause the camera  7  to hibernate or go into a low-power mode (e.g. by turning off one or more other sensors), if it receives a sensor signal from the accelerometer  5  indicating that the lifelogging device  2  has moved less than a predetermined amount during a predetermined amount of time. 
         [0061]    With each photograph, the CPU  9  may associate location data from the GPS unit  4 , orientation data from the accelerometer  5  and time (optionally including date) data from the timer  6 . The image, location, orientation and time data of the photograph are stored in non-volatile memory on the storage device  8  and transferred via the first communication device  20  to the storage service  31  of the network-based storage service  30  when a connection  50  is established between the lifelogging device  2  and the first communication device  20 . The transfer may occur during charging of the battery  10  by the charger  24  and the storage may be encrypted. 
         [0062]    The first communication device  20  may be a docking station, a Smartphone, a tablet computer, a desktop computer or a laptop computer. 
         [0063]    The connection  50 , which connects the lifelogging device  2  to the first communication device  20  via the interfaces  11  and  21 , may be a wired connection, such as a micro-USB or USB connection, or a wireless connection, such as a wireless LAN, Bluetooth®, NFC, IR, CDMA, GSM, 3G or 4G connection. 
         [0064]    The protocol used for communication between the lifelogging device  2  and the first communication device  20  may be the USB mass storage device protocol or a device-specific protocol. A device-specific protocol may comprise features making communication possible only between a specific lifelogging device  2  and a specific communication device  20 , which would make it more difficult for an unauthorized person to retrieve the data stored on the lifelogging device  2 . 
         [0065]    The connection  51 , which connects the first communication device  20  to the network-based storage service  30  via the interface  22 , may be a wired connection, such as a wired LAN connection, or a wireless connection, such as wireless LAN, CDMA, GSM, 3G or 4G connection. 
         [0066]    The protocol used for communication between the first communication device  20  and the network-based storage service  30  may be TCP/IP, HTTP, HTTPS, SSL and TLS. 
         [0067]    The network-based storage service  30  may be a REST service. 
         [0068]    The computing service  32  of the network-based storage service  30  may analyze and organize the photographs based on its image, location, orientation and/or time data. The photographs may be organized on a timeline and into groups of photographs fulfilling certain criteria, such as being from the same surroundings. The criteria may be user defined and the colors of the images may be used to determine which photographs were taken in the same surroundings. The photographs may be analyzed and their relevance assessed using criteria based on, for example, motion blur, contrast, composition, light, face recognition and object recognition. A group of photographs fulfilling certain criteria may be analyzed in order to select a photograph which is particularly representative, according to some criteria, of that group of photographs. The selected photograph may be used to give the user a rough idea of what the photographs in the group of photographs are showing and when they were taken. 
         [0069]    The user can use a second communication device  40 , for example a Smartphone, a tablet computer, a desktop computer or a laptop computer, to access the photographs and to set control parameters for the lifelogging device  2 , the network-based storage service  30  and the first communication device  20 . 
         [0070]    Control parameters may, for example, determine the image capture rate and the time dependence of the image capture rate. For example, a user may set a higher image capture rate during a certain time period of a certain day. Control parameters may also determine whether a photograph stored on storage device  31  can be accessed by other users. 
         [0071]    The user may use the second communication device  40  to perform computing functions of the computing service  32 . A computing function may be photo editing. 
         [0072]    The application software  42 , which, for example, can be a web browser or an application for smart phones or tablet computers, may be used to perform the computing functions and to set control parameters. 
         [0073]    The connection  52 , which connects the second communication device  40  to the network-based storage service  30  via the interface  41 , may be a wired connection, such as a wired LAN connection, or a wireless connection, such as a wireless LAN, CDMA, GSM, 3G or 4G connection. 
         [0074]    The protocol used for communication between the second communication device  40  and the network-based storage service  30  may be TCP/IP, HTTP, HTTPS, SSL and TLS. 
         [0075]    The network-based storage service  30  may send push notifications to the second communication device  40 , for example when photographs taken by the lifelogging device  2  have been transferred to the network-based storage service  30 . 
         [0076]    The network-based storage service  30  may send data to and receive data from devices which are not a part of the lifelogging system  2 . For example, data captured by the GPS unit  4  may be sent to a third-party which analyses the data and sends the coordinates represented by the data to the network-based storage service  30 . The network-based storage service  30  may send and receive data, for example image data, to other network-based services, for example social-networking services. 
         [0077]      FIG. 2 a    illustrates schematically a lifelogging system  1  in which the lifelogging device  2  is configured to send image, location, orientation and time data to a first communication device  20  over a connection  50  which may be a wired connection, such as a micro-USB, USB or wired LAN connection, or a wireless connection, such as a wireless LAN, Bluetooth, NFC, IR, CDMA, GSM, 3G or 4G connection. The protocol used for communicating over the connection  50  may be the USB mass storage device protocol, TCP/IP, HTTP, HTTPS, SSL or TSL or a device-specific protocol. 
         [0078]    The first communication device  20  may be a docking station, a Smartphone, a tablet computer, a desktop computer or a laptop computer. 
         [0079]    The first communication device  20  is configured to send the image, location, orientation and time data to the network-based storage service  30  over a connection  51  which may be a wired connection, such as a wired LAN connection, or a wireless connection, such as wireless LAN, CDMA, GSM, 3G or 4G connection. The protocol used for communicating over the connection  51  may be TCP/IP, HTTP, HTTPS, SSL or TSL. 
         [0080]    A user can access the data stored on the network-based storage service  30  through a second communication device  40  which is also configured to send control parameters to the network-based storage service  30  over a connection  52 . The connection  52  may be a wired connection, such as a wired LAN connection, or a wireless connection, such as a wireless LAN, CDMA, GSM, 3G or 4G connection. The protocol used for communicating over the connection  52  may be TCP/IP, HTTP, HTTPS, SSL or TSL. 
         [0081]    The control parameters sent by the second communication device  40  may comprise control parameters for the network-based storage service  30 , the first communication device  20  and the wearable lifelogging device  2 . The network-based storage service  30  transfers, over the connection  51 , control parameters to the first communication device  20  which, in turn, transfers the control parameters to the wearable lifelogging device  2  over the connection  50 . 
         [0082]      FIG. 2 b    illustrates schematically a lifelogging system  1  in which a wearable lifelogging device  2  is configured to communicate directly with a second communication device  40  and a network-based storage service  30  over connections  53  and  54 , respectively. 
         [0083]    The second communication device  40  may be a Smartphone, a tablet computer, a desktop computer or a laptop computer. 
         [0084]    The connection  53  may be a wired connection, such as a wired LAN connection, or a wireless connection, such as a wireless LAN, CDMA, GSM, 3G or 4G connection. The protocol used for communicating over the connection  53  may be TCP/IP, HTTP, HTTPS, SSL or TSL. 
         [0085]    The connection  54  which may be a wired connection, such as a micro-USB, USB or wired LAN connection, or a wireless connection, such as a wireless LAN, Bluetooth, NFC, IR, CDMA, GSM, 3G or 4G connection. The protocol used for communicating over the connection  54  may be the USB mass storage device protocol, TCP/IP, HTTP, HTTPS, SSL or TSL or a device-specific protocol. 
         [0086]    If a first communication device  20  is provided, the lifelogging device  2  may also communicate with the first communication device  20  which may be configured to communicate with the network-based storage service  30 . 
         [0087]    The first communication device  20  may be a docking station, a Smartphone, a tablet computer, a desktop computer or a laptop computer. 
         [0088]    The first communication device  20  may communicate with the be lifelogging device  2  over a wired connection, such as a micro-USB, USB or wired LAN connection, or a wireless connection, such as a wireless LAN, Bluetooth, NFC, IR, CDMA, GSM, 3G or 4G connection. The protocol used for communicating may be the USB mass storage device protocol, TCP/IP, HTTP, HTTPS, SSL or TSL or a device-specific protocol. 
         [0089]    The first communication device  20  may communicate with the network-based storage service  30  over a wired connection, such as a wired LAN connection, or a wireless connection, such as a wireless LAN, CDMA, GSM, 3G or 4G connection. The protocol used for communicating may be TCP/IP, HTTP, HTTPS, SSL or TSL. 
         [0090]      FIG. 2 c    illustrates schematically a lifelogging system  1  in which a wearable lifelogging device  2  and a network-based storage service  30  are configured to communicate over a connection  53  which may be a wired connection, such as a wired LAN connection, or a wireless connection, such as a wireless LAN, CDMA, GSM, 3G or 4G connection. The protocol used for communicating over the connection  53  may be TCP/IP, HTTP, HTTPS, SSL or TSL. 
         [0091]    Communication also occurs between the network-based storage device  30  and a communication device  40  over a connection  52  which may be a wired connection, such as a wired LAN connection, or a wireless connection, such as a wireless LAN, CDMA, GSM, 3G or 4G connection. The protocol used for communicating over the connection  52  may be TCP/IP, HTTP, HTTPS, SSL or TSL. 
         [0092]    The communication device  40  may be a Smartphone, a tablet computer, a desktop computer or a laptop computer. 
         [0093]    Referring to  FIG. 3 , a method of operating the wearable lifelogging device will now described. 
         [0094]    The method may be implemented in a finite state machine. 
         [0095]    The device may be operable in four different states. In a ready state  100 , the camera may be active in the sense that it can provide a signal indicating at least an amount of light received at the camera&#39;s image sensor, while the remainder of the device is in a low power mode. In the low power mode, one or more parts of the device may not be active, or may be active but operating at a lower clock frequency as compared to normal operation. 
         [0096]    The device may further be operable in a take photo state  200 , wherein the device wakes up from the low power mode, the camera takes a photo and optionally all sensors (e.g. accelerometer, GPS sensor, etc.) are read. 
         [0097]    The device may further be operable in a sleep state  300 , wherein the entire device is in a low power mode. In this mode, the real time clock may be active to provide a clock signal, as may those parts of the device necessary to determine whether the clock signal meets a criterion for a transition to take place. 
         [0098]    The device may further be operable in a snooze state  400 , wherein the device checks whether it should wake up (i.e. transition to the take photo state). 
         [0099]    The device may further be said to be operable in two modes: active mode, where the device shifts  110 ,  120 ,  230  between the ready state  100  and the take photo state  200  and a sleep mode, where the device shifts  310 ,  320 ,  410 ,  420  between the sleep state  300  and the snooze state  400 . 
         [0100]    From the ready state  100 , the following transitions may take place. On receipt of a signal from the clock, the device may transition  110  to the take photo state  200 . This may be the case where the device is in normal operation, i.e. takes photos at predetermined intervals, such as two photos per minute, etc. 
         [0101]    On detection of a specific movement or sequence of movements by the motion sensor or the GPS sensor, the device may transition  120  to the take photo state  200 . This may be the case where the device is arrange to detect the user tapping on the device with his/her finger in order to trigger the device to take an ad hoc photo. Hence, in this specific example, the motion sensor would sense two or more accelerations exceeding a particular threshold value within a predetermined time period, such as 1-3 seconds. Optionally the durations of the accelerations may be very short, hence indicating that the device did not move too much, e.g. that it moved less than 10 cm or less than 5 cm as a consequence of the tapping. 
         [0102]    From the take photo state  200 , the following transitions may take place. When detecting that the device is placed stationary and optionally with a specific orientation, such as horizontally, the device may transition  210  to the sleep state  300 . In this case, the device may detect an acceleration vector which is below a first threshold value T 1  (thus indicating that the device is stationary) and optionally also an acceleration vector, which may indicate that the device has been given a specific orientation, such as flat (with front or back side down) on a surface. This condition may be referred to as a “flat surface detection”. This transition  210  may be conditioned on the device having the specific orientation during a predetermined time period, such as e.g. 15, 30 or 45 seconds or 1-5 minutes. 
         [0103]    Similarly, when the camera receives light below a predetermined second threshold value T 2 , the device may transition  220  to the sleep state  300 . This transition may be referred to as a “low light detection”. This transition  220  may also be conditioned on the device receiving the low level of light during a predetermined time period, such as e.g. 15, 30 or 45 seconds or 1-5 minutes. 
         [0104]    If, when in the take photo state  200 , neither flat surface nor low light is detected, the device may transition  230  to the ready state  100 . 
         [0105]    From the sleep state  300 , the following transitions may take place. When detecting an absolute value larger than a third threshold value T 3 , the device may transition  310  to the snooze state  400 . The third threshold value T 3  may be a value indicating that the user is deliberately shaking the device in order for it to wake up. Hence, an absolute value of an accelerometer signal may be used. The third threshold value T 3  may typically be higher than the first threshold value T 1 , since that value merely distinguishes movement from stationary. In addition it is possible to set a flag F 1  to indicate that a “wake up on shake” event has occurred. 
         [0106]    The device may also transition  320  from the sleep state  300  to the snooze state based on a clock signal. This may be the case where the device is in normal operation, i.e. takes photos at predetermined intervals, such as two photos per minute, etc. 
         [0107]    The device may also transition  330  from the sleep state  300  on detection of a specific movement or sequence of movements by the motion sensor or the GPS sensor, this procedure may be substantially the same as the transition  120  to the take photo state  200  described above. Hence, an interrupt could be provided by the motion sensor, which may immediately cause the device to transition  330  from the sleep state  300  to the take photo state  200 , without going through the snooze state  400 . 
         [0108]    From the snooze state  400 , the following transitions may take place. When detecting that the device is placed stationary and optionally with a specific orientation, as described above with respect to the transition  210 , the device may transition  410  to the sleep state  300 . 
         [0109]    Similarly, when detecting a low light condition, the device may transition  420  to the sleep state  300 , as described above with respect to the transition  220  to the sleep state. 
         [0110]    If the “wake up on shake” flag F 1  is set, thus implying that the device has been shaken, and the light level is too low, the device may increase the third threshold value T 3 , thus making the device less sensitive to shaking, and then clear the “wake up on shake” flag F 1 . 
         [0111]    If neither flat surface nor low light is detected, the device may transition  430  to the take photo state  200 . In this case, the third threshold value T 3  may be reset, i.e. to normal sensitivity to shaking, and the “wake up on shake” flag F 1  may be cleared. 
         [0112]    It would be possible to provide a separate light sensor in or near the camera opening, which would enable detection of sufficient light level without making use of the camera. This could be an option for further reducing the battery consumption.