Abstract: A glass break detector for detecting the breaking of a window or the like includes an acoustic transducer having a wide band frequency response, coupled to a dual channel filter and signal processing circuit. A low frequency channel detects an initial positive compression wave caused by the inward flex of the window and a high frequency channel detects the acoustic spectrum which is characteristic of breaking glass. The two channels are combined in a logic circuit that is timed so that the low frequency positive flex is detected initially with the high frequency component following shortly thereafter. If both timing conditions are fulfilled, an alarm is initiated. Additional circuitry is provided to inhibit the alarm if a negative compression wave is initially detected. The detection sequence is initiated by a loud sound characteristic of breaking glass.