This is extremely cool: https://www.keacher.com/xmas24/

It's a PCB-based 'christmas card' with lights, except it has no battery and pulls energy from radio waves in the air, and you can both power and control it by eg. holding it next to your phone.

From what I understand, the control of the lights doesn't use any actual data connection or pairing, instead the page encodes a modulated signal directly on 2.4GHz by opening a websocket and sending / not sending data in patterns, that the card then extracts and reads!