Immobilisers

There are two types of immobilisers available to deter thieves from stealing your car. The most basic variety is the mechanical immobiliser, such as the steering wheel lock (to prevent the steering wheel from turning) or wheel clamp. These systems are usually fairly inexpensive and are easy to fit, and are ideal for using with low-risk vehicles or in conjunction with another form of security. However, their main drawback is that they do not arm automatically, and so you must remember to fit the device every time you leave the car.

Electronic immobilisers prevent the thief from starting the car by automatically immobilising the fuel pump, starter motor, ignition system or engine management system (or a combination of the four). All new cars produced since 1997 for the UK market include an electronic immobiliser, which generally makes use of a key with an internal electronic chip that provides the car with the code that will allow the engine to run. The device arms itself as soon as the key is withdrawn from the ignition, and will not deactivate without the correctly coded key. Unfortunately, if you lose your key, it can be very expensive to replace - especially if you lose the master key. Some car manufacturers may charge over £1,000 to replace a master key; however, others may be considerably cheaper.

Add-on self-arming immobilisers are widely available for imported cars or pre-1997 vehicles without factory immobilisers. Approved immobilisers must intercept at least two circuits; typically the ignition and the fuel pump, although some may also intercept the starter motor.