The red LED comes on, and NPN transistor grounds the piezo, sounding the alarm. The only way to stop it is by inserting a shorted 1/4″ phone plug conveniently attached to his key ring into a ...

So when [Martin] purchased a battery-powered smoke detector and rigged it up to notify him exactly when the piezo siren is activated, the evolution of the automatic fire alarm continued into the ...

Ideal for use in a wide range of private and commercial sites, including large complexes and multi-story buildings 110dB Piezo siren and high-power strobe light Distinguishes between fire and burglar ...