What is an immobiliser?

Last updated by mustard.co.uk on May 16th, 2019

An immobiliser can protect your car from thieves as well as help lower the cost of insurance – but what is an immobiliser, how does it work and how can you tell if your car already has one?

How does an immobiliser work?

An immobiliser is a security device that stops your car from starting if the wrong key is used. You can get electronic immobilisers and physical immobilisers which include devices like steering wheel locks.

Newer vehicles generally have electronic engine immobilisers. For your car to start, your key or key fob sends a code to a part of the car known as the electronic control unit (ECU). If the code is correct then the car will start by activating the ignition, fuel and starter motor systems.

If the code is wrong or someone tries to hotwire the car, an immobiliser will stop the car from starting by preventing the ignition, fuel and starter motor systems from working together. Immobilisers will vary by manufacturer but the basic principle behind them is the same.

What is a factory fitted immobiliser?

A factory fitted immobiliser is one that has been installed in a car during the manufacturing process.

Factory fitted immobilisers are considered more desirable than those added on afterwards because it’s assumed that a device installed at manufacture is more likely to be robust and fit for purpose.

car Immobiliser dashboard icon

Does my car have an immobiliser?

Immobilisers have been fitted as standard on all cars since 1998 so if your car is less than 20 years old, the chances are it will have a factory fitted immobiliser, unless a previous owner has taken it out or disabled it.

If your car was made before 1998, it may still have an immobiliser as some manufacturers did install them earlier than 1998, or a previous owner may have put one in. If you’re not sure, or want to find out what type of immobiliser you have, check your car handbook or ask a mechanic or engineer at your service or MOT.

What is a Thatcham device?

Thatcham Research is a not-for-profit group who work with manufacturers, trade bodies and the law to promote car security and safety standards.

In the 90s, Thatcham grouped vehicle immobilisers and car security devices into different categories which the car industry now use as benchmarks – there are eight categories in total. Security devices that aren’t Thatcham approved fall outside of these eight groups and are known as ‘Q class’ devices.

Thatcham category 1, electronic alarm and immobiliser The most secure system available with an electronic alarm and immobiliser. These systems include perimeter, glass breaking and tilt sensors. The system is passively set – which means the driver doesn’t need to do anything for it to work.
Thatcham category 2, electronic immobiliser Similar to category 1 but without an electronic alarm.
Thatcham category 2.1, electronic alarm upgrade This is where a category 2 system has been upgraded to category 1 because an electronic alarm has been added.
Thatcham category 3,mechanical immobiliser These are physical pieces of equipment rather than electronic systems – they include things like a Thatcham steering wheel lock.
Thatcham category 4,wheel locks Specialist wheel nuts used for alloy wheels are classed as a security feature because you need a special key to unlock them – which acts as a theft deterrent.
Thatcham category 5,post theft tracking Cars have a tracking device so they can be found after they’ve been stolen and can also be immobilised remotely.
Thatcham category 6,tracker Cars have a tracking device but can’t be immobilised remotely.
Thatcham category 7,tracker A more basic version of a category 6 tracker.

I’m having car immobiliser problems, what should I do?

There may be a time when your immobiliser doesn’t work properly and you find yourself unable to start your own car. It could simply be down to a flat battery in your key fob in which case, a simple battery change should resolve the problem.

If you can get into your car, but the engine won’t start, then take the key out of the ignition, leave it for a few minutes and try again. Alternatively, you could try leaving the key in the ignition to see if this reactivates the system.

car keys in ignition

Some key fobs also come with manual keys (you usually have to slide the cover off the fob). If the fob fails to work, then using the physical key should work.

If you’re still having problems with your immobiliser and you can’t start your car, it’s best to call a local garage or the dealership you got your car from.

They should be able to arrange a replacement key fob or find out if there’s a mechanical or electronic fault.

How does an immobiliser effect my car insurance?

The more secure your car is, the less likely it is to be stolen, so having an immobiliser can cut the cost of your car insurance.

If your car doesn’t have an immobiliser or you’re thinking of buying one, we recommend buying an approved Thatcham security device as these are the preferred choice for many insurers and are likely to result in the biggest premium savings.

If you want to find other ways to lower the cost of car cover, then read our guide on how to save money on your premium. Remember that when you search with us, you can be confident about getting the most for your money with our Cheapest Price Guarantee*.

You might also be interested in:

Car Security – how to prevent car theft

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