The Clicker uses radio

You can thank Nikola Tesla, for this one too. Back in 1893 he described in Patent (number 613809), named "Method of an Apparatus for Controlling Mechanism of Moving Vehicle or Vehicles". It was the first remote control of anything, TV or otherwise... predates TV of course.

Eugene F. McDonald Jr., the founder of Zenith believed TV viewers would not tolerate commercials indefinitely and was convinced that sooner or later commercial television would collapse. He was full bore behind the development of the remote so that people could avoid watching ads.

The Zenith Radio Corporation was the early leader in this arena. Before they unveiled any actual remote controls they released this weird hand held control. It didn't change channels though. It was for a 1948 Garod TV set and what it did was enlarge the picture. they called it a Telezoom. It was wired to the TV set, with a 20 foot long cable. No radio was involved.

Zenith quickly decided that people wanted to change the channel way more than they wanted to zoom in. They released the first real remote in 1950 nicknamed the "lazy bones." It too was tethered to the TV via a 20 foot cable. No radio here either.

In 1955 Zenith figured out that the tether was not popular, it was a tripwire, garrote and jump rope for children and the family pet and it had to go. They then put together the first real wireless remote. It was called the Flashmatic. It worked by shining a beam of light onto a photoelectric cell. It's major shortcoming was that the photoelectric cells couldn't distinguish between light from the remote and light from any other source. it also was very directional and required that the clicker be precisely pointed. and still no radio...

The next year Robert Adler developed the archetypal clicker, the Zenith Space Command. It too was wireless but it worked mechanically to produce ultrasonic sounds. Literally pushing a button struck a bar, each bar emitted a different frequency. The sensor in the TV received these with a microphone. The downside was that the tones were not inaudible. Both young women and dogs often would hear the shrill tones. The channel also could be changed inadvertently by naturally occurring noises. Jingling keys, xylophones and dog whistles among other things. and worse yet.. there was no radio involved at all. More here.

Here's the radio part. All remotes for your TV use either a "near" infrared diode to emit a beam of light to the device, or a radio signal. This beam/wave is a carrier wave with signals that trigger functions being it's modulated frequency. You can actually hear this work with some remotes even on the infrared carrier by playing with the clicker next to an AM radio.