One night recently, an acquaintance had a pair of quite expensive driving lights stolen from the front of his 4-wheel drive while it was parked in his driveway. For the thief, it was almost too easy - just unplug (or cut) the leads, undo a couple of mounting nuts with a shifting spanner and off you go. It's that quick!

This circuit is designed to protect your expensive driving lights and at the same time, give the prospective thief quite a scare. As soon as the power lead to the light is cut or disconnected, either the car alarm will be set off or, if you don't have an alarm, a very loud siren will be triggered. If that doesn't scare the "low-life" away, nothing will.

One important feature of this unit is that it's automatically armed each time you turn the ignition off. After all, a thief detector isn't much use if you forget to turn it on. Similarly, the unit is automatically disarmed when the ignition is switched on.

Of course, this also means that the unit isn't foolproof - if a thief "hot-wires" the car, the alarm won't sound but then you'd have much bigger problems than just a pair of stolen driving lights.