Apple introduced Touch ID for iPad Air during their September 15^th Special Event and today the U.S. Patent and Trademark Office officially granted Apple a patent for a similar Touch ID button for a future Apple Watch.

Apple's patent FIG. 1 below illustrates a view of one example of an electronic device with a biometric sensing system and button assembly; FIG. 4C is an exploded view of portions of the embodiment of a biometric sensing system; FIG. 3C is another view of portions of the embodiment of a biometric sensing system.

According to Apple's patent, the Apple Watch processor may apply the biometric identification  (fingerprint) for any of several purposes; for example, user identification, device unlocking, application authorization or to authorize a transaction. In some embodiments, the processor may also instruct the biometric sensor to capture a biometric datum from the user. Fingerprints and DNA are example biometric characteristics.

A capacitive biometric sensor may sense fingerprint characteristics of a user touch that may be used to provide a fingerprint identification of the user. In addition to providing an output that corresponds to a biometric characteristic, the output of the biometric sensor may indicate whether an input (e.g., a touch, a press, or the like) occurs, an approximate location where an input occurs, and/or a measure of the input, e.g., a measurement of absolute capacitance or capacitance change.

Review Apple's granted patent 10,866,619 for finer details.