[IshKebab]

I use these kinetic switches all the time (the Quinetic brand is great and reliable; I've tried a Chinese one once and it died after a few months).

They're good but relatively expensive and relatively large. So I can kind of see why this might make sense. On the other hand having to put ultrasonic microphones all through your house is clearly much worse than a radio receiver, so I'd say these are a bit of a gimmick still.