Passive Mobile Phone powered using Energy Harvesting
just saw this article and paper: https://blog.hackster.io/the-first-battery-free-cellphone-855307a4f30e
as usual the headline is a bit misleading; while the phone-part is completely passive, it requires as base station that does the actual mobile network communication because the RF transmission is simply too power-consuming.
Still, the mobile part draws an average of 1mW during voice calls, according to their paper (direct link to PDF at the end of the article above). I guess that's too low for any LED stuff, but it can power a microprocessor, as they have shown, and maybe it would be enough to charge a capacitor and then flash an led every once in a while, or trigger an electrode?