| 摘要 |
A battery-powered receiver having a switch for disconnecting the battery from radio frequency detection circuits within the receiver upon receipt of a sequence of coded address and command signals. Each address and command signal is a radio frequency modulated with an audio or tone frequency. A tone decoder within the receiver is sensitive to audio signals whose frequencies lie within any one of sixteen predetermined frequency ranges. Stored at the output of the decoder is an address code of two or more numbers representing tone frequencies, these numbers being representative of the particular receiver or group of receivers. A sequence of audio signals detected by the tone detector is compared with the stored address code. If the address signals are followed by a coded command signal, made up of a tone signal or sequence of tone signals, the tone detector gives an output which causes the battery switch to be opened for a time determined by the coding of the command signal.
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