Their first attempt involved ultrasonics. The remote had tuning forks or the like in them, and a button press would strike it the corresponding one.
I think it fizzled in the lab, because a woman there could hear that high up, and she thought they were deliberately annoying her. They figured if she could hear it, what about Fido...and they then figured they should find an alternative signalling method.
Our first color tv was a Heathkit, with a wired remote. Power, and a channel stepper for the VHF band. 12 at most?
RIP
I had a friend in school whose dad had one of those remotes for his console TV. It would “chunk” and then vibrate when you pressed the buttons.
Oh, it made it out of the lab.
*************************
http://en.wikipedia.org/wiki/Zenith_Electronics
The 1955 Flash-Matic remote system used a highly directional photo flash tube in the hand held unit that was aimed at sensitive photoreceivers in the four front corners of the TV cabinet. However, bright sunlight falling on the TV was found to activate the controls.
Lead Engineer Robert Adler then suggested that ultrasonic sound be used as a trigger mechanism. This was produced in the hand held unit by mechanically-struck aluminum rods of carefully constructed dimensions - a receiver in the TV responded to the different frequencies this action produced. Enough audible noise was produced by pressing the buttons that consumers began calling remote controls “clickers”. The miniaturization of electronics meant that, eventually, the sounds were produced in the remote unit electronically but the operating principle remained in use until the 1980s, when it was superseded by the infra-red light system.
Our first color set was a Heathkit as well. I still have fond memories of the hours my dad spent building it, even though he ran most of the kids out when he was working.