Oddly enough, the "energy harvesting switches" they used in this are commercial products! https://www.digikey.com/en/products/detail/zf-electronics/AF... https://switches-sensors.zf.com/us/product/energy-harvesting...
I made this slim PCB a few years ago with a super tiny NFC chip on it that can harvest energy from NFC:
Made it into a business card as you can see.
> Energy Generated: 0.33 mWs actuating and releasing
I assume it means that it generates 0.33 mWs (or mJ, come on) in a full cycle of actuating and releasing. So you have to make 3 button presses per second to generate 1 mW of power.
Around fifteen bucks each.