Have you guys use cordless electric tooth brush that charge using magnetic vibration to osculate the rechargeable battery? I use a drawing device Wacom and its electricity come from the board that transmit microwave to power the pen.

This sounds like headphone in reverse, voice or sound vibrate the diaphragm and generate electricity like a dynamo concept, I think.

Seiko have kinetic powered watch, maybe when you combine with electricity generated by sound can charge the battery but not without battery. Again much of these topic is so far from application.