Motion and gesture input from a wearable device

This invention describes a wrist-worn device that detects hand gestures by shining light onto the skin and sensing how the light changes as the underlying tissue and anatomical features move during a gesture. The device uses multiple light sensors to capture these changes. The claims specifically focus on a method for *training* the device: it prompts a user to perform a gesture, collects sensor data during that gesture, and then uses that data to teach the device to recognize that specific gesture by identifying characteristic patterns in the sensor readings.