Today we’re used to infrared remote controls, but back before modern battery technology Zenith developed the first practical remote oontrol, and it wasn’t based on infrared or radio. Dreaming of a Remote Christmas explains:
One of Zenith’s top scientists was an Austrian émigré named Dr. Robert Adler, a brilliant man who was a wizard in, among other things, high-frequency sound. In a matter of months Dr. Adler’s research team worked out an elegant solution, a purely mechanical device that required no batteries.
Adapting the principle of ultrasonics — sounds at a frequency beyond the human ear — the Adler team came up with a system of four precisely “tuned” aluminum rods. Each rod was about 2-1/2 inches long, but each was in fact cut to an exact length that gave it a unique frequency when vibrated. Above each rod was a small hammer, triggered by spring, corresponding to the four buttons. One rod’s inaudible vibration turned the set on and off, two moved the channel selector up or down, and the fourth (McDonald’s favorite) muted the sound.
Zenith was able to test and put the Space Command into production in time for the Christmas shopping season of 1956. It was expensive. It increased the cost of a Zenith television receiver by 30 percent. This was because a special ultrasonic receiver involving six vacuum tubes had to be installed in sets sold with the remote. I do not remember the exact price of the set George and I saw that day in Pittsburgh but it made my uncle, who loved technology, a bit ashen faced.