If you're old enough you might remember the Zenith Space Commander (I'm not old enough to have seen one in use).
It was an early TV remote that used spring loaded strikers controlled by buttons on the remote. The strikers hit tuned metal bars that rang out at ultrasonic frequencies the TV detected.
A links below but honestly it's the kind of topic that seems to never be covered well by a single resource. There are YouTube videos showing the inside of the controller and the striker.
[0] https://forums.atari.io/topic/10559-zenith-space-command-vin...
