That's starting to sound like an RFID device, but with sound instead of radio waves. In this framework I guess the propeller-thing is analogous to a Crookes rad

That's starting to sound like an RFID device, but with sound instead of radio waves. In this framework I guess the propeller-thing is analogous to a Crookes radiometer.[0] I wonder what would be the Great Seal Bug[1]? [0]: https://en.wikipedia.org/wiki/Crookes_radiometer https://en.wikipedia.org/wiki/Crookes_radiometer [1]: https://en.wikipedia.org/wiki/The_Thing_(listening_device) https://en.wikipedia.org/wiki/The_Thing_(listening_device)