Abstract: A security system which includes closed loop fire detection circuitry, having a continuous monitor of the pyrogenic sensors, closed loop intrusion detection circuitry, a multiple tone audible alarm generator, a coded keyboard digital electronic lock circuit, and a fail-safe alternating current, direct current power supply which includes a battery, battery charging circuit, and a system testing facility. The audible alarm circuitry includes a modulated tone frequency generator and a modulating circuit operable between a plurality of states in response to different alarm conditions. The fire and intrusion circuits include filter circuits to prevent spurious operation, and feedback latching circuits for generating continuous alarm signals in response to a breach of the system. The entire circuit is fabricated with solid state electronic components including micro-electronic circuitry.