Abstract: An alarm system for transmitting an alarm signal between remote locations utilizing frequency shift keying over conventional power lines. The alarm system includes a transmitter having a nominal frequency and circuitry for modulating the transmitter frequency. Upon detection of an alarm condition the modulating circuitry is disabled. A receiver is provided and has circuitry for detecting the presence or absence of modulation of the transmitter frequency. The receiver generates an alarm signal upon detection of absence of modulation and power failure of the system. The alarm signal is time-delayed to prevent nuisance alarms.