Remote control

The term is most commonly used to refer to a television remote control (usually just called "the remote"), although many (most?) consumer electronics come with remote controls, such as VCRs, stereo systems, and DVD players. Remote controls for these devices are usually small rectangular objects with lots of buttons for adjusting various settings such as television channel[?], track number, and volume. These remotes communicate to their respective devices via infrared signals and are usually powered by small (AA or AAA size) batteries.

In the early days of remote controls, the semiconductors for emitting and receiving infrared radiation were either inadequate or too expensive, and ultrasound was used instead. The controller contained a piezoelectric crystal that was fed by an oscillating electric current at a frequency near or above the upper limit of human hearing (but still audible by dogs). The receiver contained a microphone attached to a circuit that was tuned to the same frequency. One drawback of this method was that the receiver could be easily triggered accidentally by naturally occurring noises.

Remote controls exist for many other devices as well: model airplanes and helicopters are remotely controlled; many robots are remotely controlled, especially those which are designed for doing perilous tasks; and some state of the art military fighter jets[?] are operated by remote control.