This alarm with NO and NC sensors was found in the January 1975 Radio Electronics magazine. The circuit emits a powerful sound that depends on the output transistor.
This circuit, which appears at various points in this section and on the website with minor...
Motorola suggests this circuit in an 80's documentation. The circuit uses an inverter to produce a...
This circuit uses a 7812 and another regulator integrated circuit that is not very common...