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 can use both separate LEDs and a common cathode display when one segment indicates...
The first transformer is a driver found on transistor radios and the second a small output...
Signals of up to a few tens of kilohertz can be generated by this circuit found in a European...