Method and apparatus for off-body detection for wearable device

Abstract

A method and apparatus for capacitive off-wrist detection for wearable device are disclosed. In one aspect, the wearable device includes one or more biometric sensors including a capacitive sensor. The method may involve measuring, based on output of the capacitive sensor, a capacitance value indicative of proximity of the wearable device to a user. The method may also involve detecting a change in the capacitance value within a defined time interval, the change being greater than or equal to a threshold change indicative of the wearable device not being proximate to the user's skin. The method may further involve determining that the wearable device has been removed from the user in response to detecting that the change in the capacitance value within the defined time interval is greater than or equal to the threshold change.

1 . A method of operating a wearable device, the wearable device capable of being worn by a user and comprising one or more biometric sensors including an optical sensor configured to emit light and to detect light, the method comprising:
 emitting light from the optical sensor;   determining whether an output signal of the optical sensor is at or below an optical threshold indicative of the wearable device not being proximate to the user's skin while the light is being emitted from the optical sensor;   determining, based at least on determining that the output signal is at or below the optical threshold, whether the output signal is representative of a cardiac signal; and   determining that the wearable device is not being worn by the user based at least on determining that the output signal sensor is at or below the optical threshold and determining that the output signal is not representative of the cardiac signal.   
     
     
         2 . The method of  claim 1 , further comprising de-authenticating the user from the wearable device, the user having previously been authenticated to the wearable device, based at least on determining that the wearable device is not being worn by the user. 
     
     
         3 . The method of  claim 2 , wherein the de-authenticating of the user from the wearable device comprises preventing the wearable device from being used for a mobile payment. 
     
     
         4 . The method of  claim 2 , wherein the de-authenticating of the user from the wearable device comprises preventing the wearable device from being used for at least one of: automated teller machine (ATM) transactions; keyless entry into a vehicle; keyless starting of a vehicle; keyless entry through a door; opening of a lock; execution of an electronic signature; unlocking of a computer; automatic logging into a website; exchange of social network information; exchange of contact information; disarming of a security system; automatic upload of biometric data to an online user account associated with the user; and altering of preferences of a thermostat. 
     
     
         5 . The method of  claim 1 , wherein:
 the optical sensor is further configured to emit infrared light, and   emitting light from the optical sensor further comprises emitting infrared light from the optical sensor.   
     
     
         6 . The method of  claim 1 , wherein:
 the optical sensor is further configured to emit green light, and   emitting light from the optical sensor further comprises emitting green light from the optical sensor.   
     
     
         7 . The method of  claim 1 , further comprising:
 determining, based on the output signal of the optical sensor, at least one characteristic of the user's skin, and   calibrating, based on the determined at least one characteristic of the user's skin, an expected amount of light to be received by the optical sensor while the light is being emitted from the optical sensor, wherein the detecting whether the output signal of the optical sensor is at or below the optical threshold and the determining whether the output signal is representative of a cardiac signal are both further based on the calibrating.   
     
     
         8 . The method of  claim 1 , further comprising authenticating the user with the wearable device based at least on receiving from the user at least one of: a personal identification number (PIN); a fingerprint; biometric data; facial recognition; a password; and a pattern match. 
     
     
         9 . The method of  claim 8 , wherein the receiving is by a client device. 
     
     
         10 . The method of  claim 1 , further comprising:
 determining that the wearable device is being worn by the user based at least on either of: detecting that the output signal is above the optical threshold and determining that the output signal is representative of the cardiac signal, and   authenticating the user with the wearable device based at least on determining that the wearable device has not been removed from the user, and receiving from the user at least one of: a personal identification number (PIN); a fingerprint; biometric data; facial recognition; a password; and a pattern match.   
     
     
         11 . The method of  claim 1 , further comprising ending one or more operations of the wearable device based at least on determining that the wearable device has been removed from the user. 
     
     
         12 . The method of  claim 11 , wherein the ending of the one or more operations comprises putting at least one of the one or more biometric sensors of the wearable device into a power conservation mode. 
     
     
         13 . The method of  claim 1 , wherein the determining that the wearable device has been removed from the user is further based at least on output received from at least one of: a skin temperature thermometer; a galvanic skin response sensor; an electromyographic sensor; and an accelerometer. 
     
     
         14 . The method of  claim 1 , wherein:
 the one or more biometric sensors includes a skin temperature thermometer, and   the determining that the wearable device has been removed from the user is further based at least on output received from the skin temperature thermometer.   
     
     
         15 . The method of  claim 1 , further comprising de-authenticating the user from the wearable device based at least on determining that the wearable device is not within wireless communications range of a client device. 
     
     
         16 . The method of  claim 1 , further comprising amplifying an output of the optical sensor to create an amplified signal, wherein the amplified signal is the output signal of the optical sensor. 
     
     
         17 . The method of  claim 16 , wherein the amplifying further comprises comparing the amplified signal and a previously sampled amplified signal. 
     
     
         18 . A wearable device capable of being worn by a user, the wearable device comprising:
 an optical sensor configured to emit light and to detect light;   at least one processor; and   a memory storing computer-executable instructions for controlling the at least one processor to:
 emit light from the optical sensor, 
 determine whether an output signal of the optical sensor is at or below an optical threshold indicative of the wearable device not being proximate to the user's skin while the light is being emitted from the optical sensor, 
 determine, based at least on determining that the output signal is at or below the optical threshold, whether the output signal is representative of a cardiac signal; and 
 determine that the wearable device is not being worn the user based at least on the determination that the output signal is at or below the optical threshold and the determination that the output signal is not representative of the cardiac signal. 
   
     
     
         19 . The wearable device of  claim 18 , wherein the optical sensor is a photoplethysmographic sensor. 
     
     
         20 . The wearable device of  claim 18 , wherein:
 the optical sensor further comprises one or more light sources configured to emit one or more of: green light, infrared light, or light having multiple wavelengths, and   the memory stores further computer-executable instructions for controlling the at least one processor to emit one or more of green light, infrared light, or light having multiple wavelengths light, from the optical sensor.   
     
     
         21 . The wearable device of  claim 18 , wherein the memory stores further computer-executable instructions for controlling the at least one processor to de-authenticate the user from the wearable device, the user having previously been authenticated to the wearable device, based at least on determining that the wearable device has been removed from the user. 
     
     
         22 . The wearable device of  claim 21 , wherein the de-authentication of the user from the wearable device comprises preventing the wearable device from being used for a mobile payment. 
     
     
         23 . The wearable device of  claim 21 , wherein the de-authentication of the user from the wearable device comprises preventing the wearable device from being used for at least one of:
 automated teller machine (ATM) transactions; keyless entry into a vehicle; keyless starting of a vehicle; keyless entry through a door; opening of a lock; execution of an electronic signature;   unlocking of a computer; automatic logging into a website; exchange of social network information;   exchange of contact information; disarming of a security system; automatic upload of biometric data to an online user account associated with the user; and altering of preferences of a thermostat.   
     
     
         24 . The wearable device of  claim 18 , wherein the memory stores further computer-executable instructions for controlling the at least one processor to:
 determine, based on the output signal of the optical sensor, at least one characteristic of the user's skin, and   calibrate, based on the determined at least one characteristic of the user's skin, an expected amount of light to be received by the optical sensor while the light is being emitted from the optical sensor, wherein the detecting whether the output signal of the optical sensor is at or below the optical threshold and the determining whether the output signal is representative of a cardiac signal are both further based on the calibration.   
     
     
         25 . The wearable device of  claim 18 , wherein the memory stores further computer-executable instructions for controlling the at least one processor to authenticate the user with the wearable device based at least on receiving from the user at least one of: a personal identification number (PIN); a fingerprint; biometric data; facial recognition; a password; and a pattern match. 
     
     
         26 . The wearable device of  claim 18 , wherein the memory stores further computer-executable instructions for controlling the at least one processor to:
 determine that the wearable device is being worn by the user based at least on either of: detecting that the output signal is above the optical threshold and determining that the output signal is representative of the cardiac signal, and   authenticate the user with the wearable device based at least on determining that the wearable device has not been removed from the user, and receiving from the user at least one of: a personal identification number (PIN); a fingerprint; biometric data; facial recognition; a password; and a pattern match.   
     
     
         27 . The wearable device of  claim 18 , wherein the memory stores further computer-executable instructions for controlling the at least one processor to end one or more operations of the wearable device based at least on determining that the wearable device has been removed from the user. 
     
     
         28 . The wearable device of  claim 27 , wherein the ending of the one or more operations comprises putting at least one of the one or more biometric sensors of the wearable device into a power conservation mode. 
     
     
         29 . The wearable device of  claim 18 , further comprising at least one of: a skin temperature thermometer; a galvanic skin response sensor; an electromyographic sensor; and an accelerometer, wherein the determination that the wearable device has been removed from the user is further based at least on output received from at least one of: a skin temperature thermometer; a galvanic skin response sensor; an electromyographic sensor; and an accelerometer. 
     
     
         30 . The wearable device of  claim 18 , further comprising a skin temperature thermometer, wherein the determination that the wearable device has been removed from the user is further based at least on output received from the skin temperature thermometer. 
     
     
         31 . The wearable device of  claim 18 , wherein the memory stores further computer-executable instructions for controlling the at least one processor to de-authenticate the user from the wearable device based at least on determining that the wearable device is not within wireless communications range of a client device. 
     
     
         32 . The wearable device of  claim 18 , further comprising an amplifier electrically connected to the optical sensor and configured to amplify an output of the optical sensor to create an amplified signal, wherein the amplified signal is the output signal of the optical sensor. 
     
     
         33 . The wearable device of  claim 32 , further comprising:
 a sample-and-hold circuit; and   a differential or instrumental amplifier, wherein:
 the sample-and-hold circuit and differential or instrumental amplifier are electrically connected to the amplifier, and 
 differential or instrumental amplifier compares the amplified signal to a previously sampled amplified signal.