Alarm system and method thereof

摘要

A burglar or fire alarm is presented which cannot be disabled by cutting the power or telephone lines and which virtually cannot be radio jammed. A radio transmitter comprises an automatic switch which repetitiously and cyclically switches the carrier frequency of the transmitter between a plurality of frequencies in seriatim for transmission of an alarm signal to a distant receiver so that if at least one of the frequencies is rendered unusable by burglars by jamming or the like, the other of said frequencies will still be usable. A tape player provided with a pre-recorded message signalling an alarm condition is connected to modulate the carrier frequencies. A speed adjustment means is provided for the tape player for changing the playing time for said message. The speed adjustment permits the tape player to play back the message for transmission at a plurality of rates including an increased rate too fast for human comprehension for communication with a computer.