Abstract: An alarm detection, indication and supervision circuit with reduced power drain during failure of commerical power supply whereby standby batteries may maintain detection capability for an extended period. Separate detection and alarm indication loops are provided each with an end-of-line resistor which is removed from the circuit in response to a commercial power failure. A nearly unlimited number of detectors may be used on the detection circuit and each may have an auxiliary relay for control of local apparatus to permit local control, under changing ambient conditions. In response to an alarm signal, the potential on both loops is switched from a limited current supply to a hard supply and the polarity is reversed.