How does a remote control work?

[bluemoonKY]

I'm specifically interested in television remote controls, garage door opener remote controls, and car door remote controls.

I know that the remote control must send a signal somehow to the television, garage door, or car door respectively. But what type of signal does each type of remote control signal? I mean, is it a radio wave or what?

 

[DrClaude]

http://en.wikipedia.org/wiki/Remote_control

 

[Mike_In_Plano]

Different ones use different techniques. TV remote controls are fairly fun and straight forward. They typically switch an infrared LED on and off at a 44kHz rate. A receiver in the TV picks up infrared and is tuned to 44kHz.
The 44khz signal is called a carrier. Using it helps the TV distinguish the difference between steady sources of light, like sunlight, and the remote.
To get message across, the carrier is turned of and on in a sequence that's unique to the TV brand and function.
Garage doors and cars do the same thing with a radio signal (the carrier), but most of these remotes only use each code once and then move to another code in a very long list. The opener or car only uses each code once, and then rejects it from there on. This keeps thieves from using a receiver to steal the code and reuse it.

Left over remotes are pretty common. I really encourage you to take one apart to look at. You'll find a little LED in the TV/VCR/Cable remotes, and a loop in car remotes that is used as an antenna.

-Mike