Multipurpose wearable electrical contact

1. A wearable device, comprising:

a housing;

a rechargeable battery;

a mount configured to mount the housing to an external body surface;

first and second electrical contacts protruding from the housing, wherein the first and second electrical contacts are configured to contact skin at the external body surface when the housing is mounted on the external body surface; and

electronics, wherein the electronics comprises:

a recharger configured to recharge the rechargeable battery, wherein the recharger is configured to be powered through the first and second electrical contacts; and

a GSR sensor configured to obtain a measurement relating to a Galvanic skin resistance (GSR) of the skin at the external body surface via the first and second electrical contacts, when the recharger is not being powered through the first and second electrical contacts, wherein the GSR sensor comprises:

a reference voltage source configured to provide a reference voltage relative to the second electrical contact;

a resistor connected between the reference voltage source and the first electrical contact, wherein the resistor has a reference resistance; and

a voltage sensor coupled to the first electrical contact, wherein the voltage sensor is configured to sense a voltage between the first and second electrical contacts, wherein the voltage is related to the reference voltage, the reference resistance, and the GSR of the skin at the external body surface.

2. The wearable device of claim 1 , wherein the electronics further comprises:

a rectifier connected between the recharger and the first electrical contact, wherein the rectifier is configured to be forward biased when the recharger is being powered through the first and second electrical contacts and to be reverse biased when the recharger is not being powered through the first and second electrical contacts,

wherein the GSR sensor is configured to obtain the measurement relating to the GSR of the skin at the external body surface, via the first and second electrical contacts, when the rectifier is reverse biased.

3. The wearable device of claim 2 , wherein the rectifier comprises a diode.

4. The wearable device of claim 2 , wherein the rectifier comprises a transistor.

5. The wearable device of claim 1 , wherein the voltage sensed by the voltage sensor when the housing is mounted on the external body surface is a fraction of the reference voltage, wherein the fraction corresponds to the GSR of the skin divided by a sum of the GSR of the skin and the reference resistance.

6. The wearable device of claim 1 , further comprising a user interface configured to provide a user-discernible indication of the GSR.

7. The wearable device of claim 1 , further comprising a wireless communication interface configured to transmit data indicative of the GSR.

8. The wearable device of claim 1 , wherein the GSR sensor further comprises an amplifier and an analog-to-digital converter.

9. The wearable device of claim 1 , wherein the external body surface is a wrist location.

10. The wearable device of claim 1 , wherein the first and second electrical contacts are separated by a distance of between 1 millimeter and 50 millimeters.

11. The wearable device of claim 1 , wherein the first and second electrical contacts are spring-loaded.

12. The wearable device of claim 1 , wherein the housing is configured to be water-resistant, wherein the first and second electrical contacts are configured to protrude from the housing such that the housing is water-resistant.

13. A method, comprising:

charging a wearable device via first and second electrical contacts protruding from a housing of the wearable device, wherein charging the wearable device comprises forward biasing a rectifier in the wearable device and powering a recharger in the wearable device through the forward biased rectifier, wherein the recharger is configured to recharge a rechargeable battery in the wearable device;

mounting the wearable device to an external body surface such that the first and second electrical contacts contact skin at the external body surface; and

obtaining, using a GSR sensor in the wearable device, a measurement relating to a Galvanic skin resistance (GSR) of the skin at the external body surface via the first and second electrical contacts while the rectifier is reverse biased, wherein the GSR sensor comprises a voltage sensor electrically connected to the first electrical contact and a reference voltage source electrically connected to the first electrical contact through a resistor having a reference resistance, wherein obtaining the measurement comprises:

the reference voltage source generating a reference voltage relative to the second electrical contact, such that a fraction of the reference voltage appears across the first and second electrical contacts, the fraction being related to the GSR and the reference resistance; and

the voltage sensor measuring a voltage between the first electrical contact and the second electrical contact, wherein the measured voltage corresponds to the fraction of the reference voltage.

14. The method of claim 13 , wherein the wearable device comprises a processor, further comprising determining, using the processor, the GSR of the skin at the external body surface based on the measurement obtained using the GSR sensor.

15. The method of claim 14 , wherein determining the GSR of the skin at the external body surface based on the measurement obtained using the GSR sensor comprises determining a multiple of the reference resistance, wherein the multiple corresponds to the measured voltage divided by a difference, wherein the difference corresponds to the measured voltage subtracted from the reference voltage.

16. The method of claim 14 , further comprising indicating the determined GSR using a display disposed in the wearable device.

17. The method of claim 14 , further comprising wirelessly indicating the determined GSR using a wireless transmitter disposed in the wearable device.

18. The method of claim 14 , further comprising operating the wearable device based on the determined GSR.