Funny, we discovered our TV's remote was ultrasonic when we could turn it off with a Slinky. "Rolling" the Slinky back and forth fast enough between two hands created a high metallic sound and we figured the remote must be emitting ultrasound for that to work--we just didn't think about how it worked before. I guess the off frequency was the lowest because we could never get it to do anything else, just turn off.

My honest Sesame Street story: before we had a TV (my parents didn't want one in the house) I was allowed to go to a neighbor's house on Saturday morning to watch with them. One time when I was about 5 years old, I showed up early (7am, 8am?) and just let myself in and turned on the TV before they got up. They would watch Sesame Street, but I never really liked the characters, I just didn't get why there were muppets and monsters living with people in a real city, it just seemed so made up (of course, now I see it as a race/not-race thing). Maybe it was too urban and didn't relate to my suburban upbringing. But I loved the pinball animation (except for the repeated counting and numbers): https://www.youtube.com/watch?v=VOaZbaPzdsk