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 that triggers an SCR was found in volume 5 of the 1995 Encyclopedia of Electronic Circuits....
This 1-transistor oscillator circuit was found in the March 1965 Radio Electronics magazine. The...
Found in a 1964 CQ magazine this circuit consists of an automatic telegraphic key, providing the...