There's at least some power to be pulled from ambient radio waves. No idea if it would be enough to power these things. https://phys.org/news/2017-08-ambient-e

There's at least some power to be pulled from ambient radio waves. No idea if it would be enough to power these things. https://phys.org/news/2017-08-ambient-energy-power-internet.html https://phys.org/news/2017-08-ambient-energy-power-internet.... Or combine it with photovoltaics: https://www.smart2zero.com/news/self-powered-camera-sensor-combines-imaging-energy-harvesting https://www.smart2zero.com/news/self-powered-camera-sensor-c...