Inside the Remote
When a button on a television or DVD-player remote is depressed, it completes a specific circuit on the circuit board inside the remote. Each button has its own circuit, which sends electric pulses to a light-emitting diode (LED) on the remote's front. The LED gives off infrared (IR) light---light in a spectrum beyond the range of human vision. The LED will flash pulses of such light, in a pattern specific to the button that has been pressed.
Communication With the Device
The television or player is equipped with an infrared-sensitive receiver, situated on the front of the device. When a specific pulse of light is received, the device interprets this into a binary code, which is sent through its circuitry to perform the specified operation, such as adjusting the volume or changing channels. Together with the button-specific pulses of light, the remote sends a device-specific pulse, common with all the buttons on the remote, but unique to the brand of DVD-player or TV. This is so that the device knows that the signal sent is meant for itself---preventing confusion between your television, VCR, and other remotely controlled devices in the same room.
Limitations of IR
Most infrared remote controls have a range of less than 30 feet. At ranges greater than this, the device's receiver cannot properly detect the pulses of light sent to it. Because IR remotes communicate with light, no object can be placed between it and the receiver, for communication to work. Additionally, the remote usually has to be pointed almost directly at the receiver for the light to be properly picked up, unless the remote has large or multiple LEDs.
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