The first TV remote control called “Lazy Bones” was developed by Zenith Radio Corporation in 1950 and was connected to the television by a wire. A wireless remote control called the “Flashmatic”, was developed in 1955 but did not function well because the pointer beam (based on photoelectric cells) could not distinguish between different light sources.
In 1956, Robert Adler developed “Zenith Space Command”, a wireless remote which used ultrasound to change the channel and volume. When the user pushed a button on the remote control, it clicked and struck a bar. This is where we get the term “clicker”. Each bar emitted a different frequency and circuits in the television detected this sound. (Wikipedia)