WEARABLE ELECTRONIC DEVICE

1 .- 20 . (canceled)

21 . An electronic watch comprising:

a housing defining a first opening and a second opening;

a display positioned at least partially within the first opening;

a front cover positioned over the display and at least partially defining a front exterior surface of the electronic watch;

a biosensor module positioned at least partially within the second opening and comprising an optical sensor;

a rear cover defining:

an optically transparent window aligned with the optical sensor of the biosensor module; and

at least a portion of a rear exterior surface of the electronic watch opposite the front exterior surface;

a first electrode positioned along the rear exterior surface of the electronic watch; and

a second electrode positioned along a side exterior surface of the electronic watch, wherein:

the electronic watch is configured to measure a heart rate using light transmitted through the optically transparent window of the rear cover; and

the electronic watch is configured to measure an electrocardiographic characteristic using the first electrode and the second electrode.

22 . The electronic watch of claim 21 , wherein:

the electronic watch further comprises an input device positioned along the side exterior surface of the electronic watch; and

the input device comprises the second electrode.

23 . The electronic watch of claim 22 , wherein the input device is a crown configured to receive rotational and translational inputs.

24 . The electronic watch of claim 21 , wherein:

the electronic watch further comprises a third electrode positioned along the rear exterior surface of the electronic watch; and

the electronic watch is configured to measure the electrocardiographic characteristic using the first electrode, the second electrode, and the third electrode.

25 . The electronic watch of claim 24 , wherein:

the optically transparent window is positioned at a central region of the rear exterior surface of the electronic watch; and

the first electrode and the third electrode are positioned at a peripheral region of the rear exterior surface that surrounds the central region.

26 . The electronic watch of claim 21 , wherein:

the optical sensor is one of an array of optical sensors; and

the rear cover defines an array of optically transparent windows, each window of the array of optically transparent windows aligned with a respective optical sensor of the array of optical sensors.

27 . The electronic watch of claim 21 , wherein:

the optical sensor comprises:

a light source; and

a detector;

the detector is configured to measure a change in light absorption by a region of skin of a user;

the electronic watch is configured to compute the heart rate using the measured change in light absorption; and

the display is configured to display information associated with the heart rate and the electrocardiographic characteristic.

28 . A wearable electronic device comprising:

a housing;

a band attached to the housing and configured to couple the wearable electronic device to a user;

a touch-sensitive display positioned at least partially within the housing;

a rear cover positioned at least partially within a rear opening defined along a rear portion of the housing, the rear cover defining an optically transparent window along a rear exterior surface of the wearable electronic device;

an optical sensor positioned within the housing and configured to transmit an optical signal through the optically transparent window;

a first electrode positioned along the rear exterior surface of the wearable electronic device; and

a second electrode positioned along the rear exterior surface of the wearable electronic device, wherein:

the first electrode and the second electrode at least partially surround the optically transparent window;

the wearable electronic device is configured to measure a heart rate using the optical sensor; and

the wearable electronic device is configured to measure an electrocardiogram using the first electrode and the second electrode.

29 . The wearable electronic device of claim 28 , wherein:

the wearable electronic device further comprises a crown positioned along a side exterior surface of the wearable electronic device;

the crown is configured to receive a rotational input and a translational input;

the touch-sensitive display is configured to receive a touch input;

the touch-sensitive display is responsive to the rotational input, the translational input, and the touch input; and

the touch-sensitive display is configured to display information associated with the heart rate and the electrocardiogram.

30 . The wearable electronic device of claim 29 , wherein:

the crown comprises a third electrode; and

the wearable electronic device is configured to measure the electrocardiogram using the first electrode, the second electrode, and the third electrode.

31 . The wearable electronic device of claim 28 , wherein the rear cover protrudes from the housing to contact skin of a user while the wearable electronic device is worn.

32 . The wearable electronic device of claim 28 , wherein:

the optically transparent window is positioned in a central region of the rear exterior surface of the wearable electronic device; and

the first electrode and the second electrode are positioned in a peripheral region of the rear exterior surface that surrounds the central region.

33 . The wearable electronic device of claim 28 , wherein:

the rear cover is formed from a transparent substrate; and

the transparent substrate comprises one or more of a glass or a sapphire material.

34 . The wearable electronic device of claim 28 , wherein:

the rear cover defines a convex exterior profile; and

the convex exterior profile facilitates alignment between the rear cover and a mating surface of an external wireless charging device.

35 . An electronic watch comprising:

a housing at least partially defining a side exterior surface, and a rear exterior surface of the electronic watch;

a display positioned at least partially within the housing and configured to produce a graphical output that is viewable along a front exterior surface of the electronic watch opposite the rear exterior surface;

an input device positioned along the side exterior surface and comprising a first electrode; an optically transparent window positioned in a central region of the rear exterior surface;

a biosensor module positioned at least partially within the housing and configured to detect a signal through the optically transparent window;

a second electrode positioned in a peripheral region of the rear exterior surface, the peripheral region at least partially surrounding the central region of the rear exterior surface; and

a third electrode positioned in the peripheral region of the rear exterior surface, wherein:

the electronic watch is configured to measure a heart rate using the biosensor module, and

the electronic watch is configured to measure an electrocardiogram using the first electrode, the second electrode, and the third electrode.

36 . The electronic watch of claim 35 , wherein:

the electronic watch further comprises:

a front cover positioned over the display; and

a rear cover positioned over the biosensor module; and

the optically transparent window is defined within the rear cover.

37 . The electronic watch of claim 36 , wherein:

the display is a touch-sensitive display configured to detect a touch input on the front cover; and

the electronic watch is configured to measure the electrocardiogram in response to receiving the touch input.

38 . The electronic watch of claim 35 , wherein:

the input device is a button configured to receive a translational input; and

the electronic watch is configured to measure the electrocardiogram in response to receiving the translational input.

39 . The electronic watch of claim 35 , wherein:

the input device is a crown configured to receive a translational input and a rotational input; and

the electronic watch is configured to measure the electrocardiogram in response to receiving at least one of the translational input or the rotational input.

40 . The electronic watch of claim 35 , wherein:

the optically transparent window is a first optically transparent window;

the electronic watch further comprises a second optically transparent window; and

the biosensor module comprises:

a light source configured to emit light toward a region of skin of a user through the first optically transparent window: and

a detector configured to receive light reflected from the region of the skin through the second optically transparent window.