Radio waves & vibrations... what's the first thing that comes to mind? Batteries, duh

Bye-Bye Batteries: Radio Waves as a Low-Power Source

Using only radio waves for its electrical power, the SmartHat has a beeper that alerts the wearer to dangerous construction equipment nearby.

Vibration-powered Generators Replace AA, AAA Batteries

For example, when the generator, which the company calls "Vibration-powered Generating Battery," is set inside a remote control, it is possible to use the remote by shaking it to generate power.