Security system with saw transmitter

Abstract From the Canadian patent

An electronic security system having sending units for transmitting signals representative of a condition, such as fire smoke, intrusion, or an, emergency, to a central alarm station. The sending units include detectors for producing the condition signals and an electric oscillator circuit for producing an r-f signal in an antenna. A feedback subcircuit of the oscillator circuit includes a surface acoustic wave resonator (SAWR) for stabilizing the oscillations. A circuit including a voltage variable capacitor is responsive to the condition signal to frequency modulate (FM) the r-f signal. The central station receives the modulated r-f signal and decodes it to produce an output indicative of …