SCHMITT TRIGGER LOUD ALARM WITH FEEDBACK

An alarm system circuit comprises a logic array comprising a piezoelectric transducer driven by one or more Schmitt triggers. The logic array operates at substantially resonant frequency, and the circuit provides a feedback loop to sustain the oscillations of the logic array to drive the transducer. In one preferred embodiment, the array includes an additional Schmitt trigger causing the circuit to toggle on and off, thus making a pulsating tone.