Networks of small sensors monitor everything from soil and buildings to logistics, but replacing their batteries is a chore and creates waste. Many now harvest energy from light, including indoor light, powering themselves and trickling charge into a small store so they can run for years untouched.
Self-powered sensors make large monitoring networks far more practical, since no one must visit each device to swap batteries. They suit low-power tasks that send small amounts of data occasionally, and performance depends on available light, so they are matched to the right jobs, but they remove a major obstacle to deploying sensors widely and leaving them in place.