Woman hand inserting key in car door.

What is a car immobiliser and does my car have one?

Car immobilisers play an important role in making your car protected from theft. Learn more about this essential protection piece for your vehicle in this article written by Charlie Harvey from Car Buyer.

It’s easy to take car security for granted these days, with advanced car alarm systems and tracking devices available on more modern cars. Car immobilisers have played a vital role in reducing vehicle theft for many years. Still, while they are included on all modern cars, immobilisers haven’t always been fitted as standard.

An electronic car immobiliser is one of the most essential pieces of car security technology; an extra line of defence to stop your car from being stolen. With an immobiliser, the car key needs to fit the lock and be programmed before the car’s computer system recognises it as the correct key.

Modern car keys are more expensive to replace than old car keys. Whereas you may have been able to cut a new key for an older car, modern ones require you to have the key synced with their computer before starting the engine.

The technology has existed for a long time but only became mandatory for all new cars in the UK in 1998. Suppose your vehicle was made before 1998 or was imported from another country where immobilisers were not standard when the car was produced. In that case, you might not have an immobiliser in your vehicle. Vehicles with a factory-fitted immobiliser are more secure and usually cheaper to insure. Fitting an aftermarket immobiliser can also lower the cost of your insurance premiums.

Worry-free car leasing

The Motability Scheme makes leasing a car an easy, hassle-free experience. With the Scheme, you can exchange part or all of your qualifying mobility allowance to lease a brand-new vehicle of your choice.

Insurance, breakdown assistance, servicing and maintenance is already arranged and included in the price you pay, so you can enjoy the freedom that comes with a worry-free lease.

The term ‘immobiliser’ is most commonly referred to electronic devices, but disk-locks and steering wheel clamps are also technically a type of immobiliser, known as ‘mechanical immobilisers’. These are less secure than electronic immobilisers as they can be easier to locate and be removed.

How does an immobiliser work?

Most electronic car immobilisers work by cutting off the car’s starter motor, fuel system, ignition systems or combination of the three until the correct key is used to start the vehicle. The car’s key is not only cut to fit the lock on the ignition cylinder, but it also contains a small computer chip with a code called a transponder, which disables the immobiliser once the key is turned.

Nowadays, most cars’ immobilisers work ‘passively’, meaning the owner does not need to set or arm them, although some much older cars require the driver to arm them manually. Passive systems are safer as they eliminate the possibility of forgetting to secure your vehicle. But it also means you might not be able to tell if your car has an immobiliser installed.

What is a Thatcham-approved immobiliser?

During the early 1990s, car thefts and break-ins were a serious epidemic. Thatcham, a car product research centre, launched its alarm and immobiliser categories to address this issue by informing car buyers what levels of car security equipment were installed on a car and setting an industry benchmark to improve car security. 

The Thatcham category system is fairly complicated, but as a general rule, the lower the category number, the higher the standard of security offered. Thatcham category 1 means the car has an alarm and immobiliser fitted, whereas category two just means an electronic immobiliser is installed. Category 2/1 means the car was fitted with an aftermarket alarm system to improve and upgrade security. Category 3 systems refer to more basic mechanical immobilisers like steering wheel clamps and disk-locks.

If your car was made after 1998, the likelihood is it has an immobiliser because it became mandatory in the UK. If your vehicle is older and you’re unsure if your car has an immobiliser or want to know what other security equipment is fitted, you can check Thatcham’s website to see if one was fitted from the factory.

Suppose your car didn’t come as standard with an alarm or immobiliser, but you later had them fitted. In that case, many insurers will reduce your premium depending on which category of immobiliser you’ve had installed.


This article was written by Charlie Harvey from Car Buyer and was legally licensed through the Industry Dive Content Marketplace. Please direct all licensing questions to legal@industrydive.com.

Related Articles

Car Security: top tips

Car Security: What you need to know

Could we see smartphones replacing car keys?

From the Motability Scheme


Related articles

Popular articles