This immobilizer circuit for the car was found in the Radio Electronics magazine of December 1976. It has several sensors blocking the ignition system.
In the figure we have the way to use a stepper motor as an encoder. Operational amplifiers can be of...
Placed inside the refrigerator, this circuit triggers an oscillator when the part is opened...
We found this circuit in an old documentation from the 70s, but it can be assembled with more...