This alarm circuit triggers when S1 opens. The circuit from a January 1975 Radio Electronics magazine can be used with interrupt sensors connected in series.
Found in American documentation from the 90s, this circuit shows how to derive a signal in the...
Found in a 90s American documentation, this circuit is used in vehicles with contact breaker. The...
This circuit was found in the January 1994 Electronics Now magazine. The transistors are general...