This circuit was found in an 80's Electronic Engineering. The circuit uses operatives of the time that are not common today. The power supply must be symmetrical.
Found in Popular Electronics this circuit will trigger a buzzer if the ignition key is removed...
This circuit is from an English publication from 1973, but can be easily assembled today. 2N718 can...
The figure shows how to connect a relay to obtain the latch effect. The circuit is from an...