Sixty years ago this month, the May 1965 issue of Popular Electronics showed this simple circuit for a headlight reminder. I remember that starting in the 1970s, cars started including a noisemaker to remind you of various things, such as not wearing your seat belt. But the one helpful thing it could be used for would be to prevent leaving your headlights turned on.

The circuit shown here is simplicity itself. All you needed was a buzzer, a diode (the cheapest one you could find) and a resistor (unless you had a 6-volt car, in which case the resistor could be omitted). You connected one side to the light switch, and the other two the ignition switch. If both the lights and the ignition were turned on, then there would be zero voltage difference, and the buzzer would be quiet. If the ignition were on and the lights were off, then the diode would block the flow of current. But if the lights were on and the ignition was off, then current would flow and the buzzer would sound.