This circuit, with a 12 V input, was found in a Popular Electronics from the 1990s. Information is given about the ferrite-wrapped transformer. The transistor must be mounted on a heatsink.
This alarm circuit was found in the July 1992 Radio Electronics magazine. The circuit uses a small...
The circuit shown is from a 1972 publication. Transistors can be current types like 2N2222. The...
Found in an Electronics Now from the 1980s, this circuit is based on grid leakage current for...