Ignition kill switches are one of the cheapest and most effective means of protecting your car. In simplest terms they are a switch inserted somewhere into your ignition circuit that stops the circuit from being completed without the switch being on.
This means that the would-be thief must find and activate the switch before he can start the car. These switches can be infuriating for thieves as they may have done everything else to override the cars security but cannot start the car for an unknown reason.
Switches can easily be installed yourself, or by a qualified vehicle electrician, and should be in a hidden location that would not be easily found by criminals. Almost any sort of electrical switch can be used, and are incredibly cheap to buy from any electrical hardware store. If you can source one that requires a key to activate then even better. Do not advertise the fact that you have a kill switch fitted or criminals will just go looking for it.
Just remember to switch the system off when you leave the car, and remember you’ve got it fitted when you get back in. This is an ideal system for older cars where an electronic immobiliser system may be too expensive, and works great in tandem with a mechanical immobiliser to provide visual discouragement.