This circuit was obtained from an American 1980s documentation. The frequency depends on the crystal and the circuit may be a PNP that reaches the generated frequency.
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...