The small size of touchscreens on smartwatches makes interaction cumbersome, motivating the need for touch interaction beyond the perimeter of a wrist-worn device. This thesis presents TouchPoint, a wrist-worn sensor device and processing algorithms that return a positional measurement of a finger touching the back of the hand, an interactive area that is accessible and discreet. In addition to maintaining sub-millimeter precision and sub-centimeter positional accuracy, the developed solution requires no prior calibration for use. Designed with the aim to be deployable in a consumer smartwatch form factor in mind, the system takes steps towards being appropriately miniature, low power, unobtrusive, and comfortable. Applications of the device design can be easily extended to other tracking applications with similar geometric constraints such as tracking a finger or pen-like tool on a table surface next to a phone or laptop, or serve as an always-accessible interactive surface to control ubiquitous Internet-of-Things devices.
