This circuit is activated by the ignition key which, when removed, makes a relay beep if the lights are on. Note that in this circuit, the relay itself used as an oscillator. The circuit is from a Popular Electronics from the 90s.

This circuit is activated by the ignition key which, when removed, makes a relay beep if the lights are on. Note that in this circuit, the relay itself used as an oscillator. The circuit is from a Popular Electronics from the 90s.