| 摘要 |
A system for monitoring a location for the occurrence of a predetermined condition thereat includes a transmitter located at the monitored location for normally transmitting a series of first electrical signals at a first repetition rate and in a first time slot; a sensor at the monitored location for sensing the predetermined condition; and a control circuit effective, upon sensing the predetermined condition, to interrupt the transmission of the first electrical signals and to initiate the transmission of a series of second electrical signals at a second repetition rate and in a second time slot both having a predetermined relation to the first repetition rate and the first time slot of said first electrical signals.
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