They're actually not piezo-powered! That's an EnOcean switch module, it's generating the energy from a coiled wire. Clicking the switch loads up force in a spri

They're actually not piezo-powered! That's an EnOcean switch module, it's generating the energy from a coiled wire. Clicking the switch loads up force in a spring mechanism and then releases it to move a magnet through the coil. ArsTechnica has a look inside a similar module in the Hue Tap. https://arstechnica.com/gadgets/2014/08/gallery-dissecting-the-philips-hue-tap-wireless-battery-less-controller/ https://arstechnica.com/gadgets/2014/08/gallery-dissecting-t... RunLessWire looks to be selling two variants of them, one with the same 2.4 GHz module as above for use with Hue, and another version for on/off circuit control, which would be 902 MHz EnOcean in the US.