This CMOS integrated alarm was found in the July 1992 Radio Electronics magazine. The circuit has a small power stage and its sensitivity is adjusted at R5.
This circuit is from an English magazine of 1977. The circuit is still current, just using BC547...
This circuit was obtained in an old Elektor. It is a reference, since the integrated products of the...
This circuit was found in a European technical documentation from 1991. It is a circuit that must...