M3720-4-Siren-Generator-IC-Tru Semi-M3720-4-A-simple-one-key-siren-generator-that-only-requires-a-few-external-components-to-produce-a-working-circuit-If-required-the-LED-&-resistor-on-pin-4-can-be-removed-&-replaced-by-a-small-value-electrolytic-capacitor-M3720-4-1-key_-1-siren-Ic