"By pressing a button on the remote, you set off a spring-loaded hammer that strikes a solid aluminum rod in the device, which then rings out at an ultrasonic frequency. "
I had one of these TVs when I was a kid, it came from my grandparents' house when they got a new one. We also had a dog that wore a steel-linked choker collar, and the TV channels would change, or the TV would turn on an off when he ran around and jangled the collar.