A self-powered module for gesture recognition is presented that utilizes small, low-cost photodiodes for both energy harvesting and gesture sensing. Operating in the photovoltaic mode, photodiodes harvest energy from ambient light. In the meantime, the instantaneously harvested power from individual photodiodes is monitored and exploited as a clue for sensing finger gestures in proximity. Harvested power from all photodiodes is aggregated to drive the whole gesture-recognition module including a micro-controller running the recognition algorithm. A robust, lightweight algorithm is provided to recognize finger gestures in the presence of ambient light fluctuations. Two prototypes are fabricated to facilitate user's interaction with smart glasses and smart watches.