Abstract: An automatic siren silencing device for false alarms, for use in an alarm system having a siren driver which powers a siren. A microcomputer monitors pulse signal characteristics of the siren driver, including duration of pulses and number of pulses, and compares these characteristics with predetermined pulse signal characteristics stored in a memory. A relay coil is energized by the microcomputer, controlling a relay switch which disconnects the siren from the siren driver when the pulse signal characteristics are indicative of a false alarm thereby silencing the siren. A user means is provided to adjust the predetermined pulse signal characteristics. Power to the microcomputer is provided by a capacitor, charged by the signal of the siren driver, whereby no battery or dedicated external power supply input is required. Indicator lights and a piezo element inform a user of siren silencing, and indicate the types of false alarms detected.