You are correct about the ultrasonic remotes. My parents purchased a home from a friend and the house had a black and white Zenith TV in the basement. He had removed the TV from its cabinet and cut a hole in the wall so that the TV was mounted flush in-wall. There was a 60 gallon aquarium installed above the TV, also custom fitted flush in the wall. No danger there.

The TV used one of those ultrasonic remotes for channel and volume. We got a real kick out of it as kids. Pretty sure that old TV still worked when they sold the place.