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What is an immobiliser?

One tip that crops up a lot is ‘make sure you beef up your car security with an immobiliser and alarm’. It's one of the most common ways to keep your car secure from thieves

But what is an immobiliser, how can you make sure you have one, and what are the best alarms and trackers for the job? Here’s what you need to know.

Thief trying to disarm car security


What is an immobiliser?

A car immobiliser is a device that only allows your car to start if you’re using the correct key or fob. This means that your car is protected against hotwiring from would-be thieves. 

A factory-fitted immobiliser is generally considered to be the best kind. That means it’s been installed by the manufacturers, so is more likely to function properly.

Factory-fitted immobilisers have been compulsory on all new vehicles in England and Wales since October 1998. But if you’ve got an older car or buy a second-hand car, you could find your vehicle doesn’t have one.


How do immobilisers work?

When you get in your car, the key or fob sends an electronic code that allows your vehicle to start. This means that if a thief tries to use an incorrect key, the car shouldn’t work. Typically, the car immobiliser disables 2 of 3 components:

  • Fuel system

  • Starter motor

  • Ignition


Does my car have an immobiliser?

If your car was made after this 1998, you should be safe in the knowledge that you’ve got a car immobiliser.

If your car is older than this, have a check. Some might have been fitted with an immobiliser at the factory, and others might have had them installed later.

The easiest thing to do is check your owner’s handbook. Failing that, you can contact the manufacturer, or ask a qualified mechanic to check for you.


Can an immobiliser be defeated?

Having a car immobiliser certainly makes your car more secure, but it doesn’t prevent it being stolen altogether. Thieves could still tow away a car, for example.

And keyless car theft, where relay technology is used to steal vehicles, is on the rise. Installing a wheel lock, adding an alarm and even putting your fob in a faraday pouch could all help make sure your car is even more secure.


Common immobiliser problems

Faulty engine immobilisers are rare, but when it does happen it could cause car problems and major headaches for drivers.

Typical issues include:

  • Unlocking problems

  • Locking problems

  • Engine start problems

  • Keys that don’t turn in the ignition

  • Car alarm problems

If you’re having issues the first port of call is to change the battery in your fob. If that doesn’t work, you should contact the dealer or garage where you bought the vehicle.


Other car alarms and trackers

If you want to keep your car safe, you might want an alarm and tracker on top of a car immobiliser. There are a few types to consider, and some might come installed as standard when you get a new car.

These are the three main options:

Audible alarm systems

These are the alarms we typically think about that make a loud noise if someone tries to break into your car. If you buy a new vehicle, it’s likely that it has an audible alarm installed already.

The alarms are useful, as they might scare off any criminals. But one downside is people have a tendency to ignore them as they might go off accidentally.

Silent alarm systems

These alarms also go off when someone tries to break into your car, but they don't make a sound. Instead, you're alerted as the owner. At that point, you could ring the police and tell them your vehicle is being stolen.

You shouldn’t try and intervene on your own as it could be dangerous.

GPS tracking

Trackers probably aren't going to stop your car being stolen, but they could help you get your vehicle back. Typically, they use GPS to show you where your car is in real time.


What is a Thatcham device?

Thatcham is an independent institution that rates car security and helps insurance companies factor this into their car insurance price calculations.

Thatcham has 7 different classes for car security. The closer to first class you get, the more robust your security is and lower you might be able to push your car insurance costs.

Class 1 – electronic alarm and immobiliser

The most complex and secure system on the market. Class 1 alarms often run on their own battery supply, and engine immobilisers have the ability to activate on their own. Both immobiliser and alarm have to be present for class 1.

Class 2 – electronic immobiliser

This is a class 1 car immobiliser but without the alarm. For class 2, it needs to be able to disable 2 of the 3 systems used to drive the car.

Class 2/1 – electronic alarm upgrade

If you have an immobiliser, you can add a class 1 alarm afterwards. Though this doesn’t push you into fully-fledged class 1 territory, it’s as close to it as you’ll get without getting a new car.

Class 3 – mechanical immobiliser

The most common kind of class 3 feature is a steering wheel lock. Class 3 features disable only 1 of the 3 systems used to drive a car. You need to fit these every time you want to secure the car.

Class 4 – wheel locks

If you’ve got a set of shiny alloys, you likely have wheel-locking nuts on them. These nuts can only be removed using a special key, making them harder to steal.

Class 5 – post-theft tracking

If your car is stolen, this system tracks its position so that the police can recover it. They also have the ability to immobilise the car remotely.

Class 6 – tracker

This is a class 5 tracker but without the ability to remotely immobilise the car.

Class 7 – tracker

A more simplistic version of a class 6 tracker that allows police to recover a stolen car.

There’s also a Q class that covers aftermarket security upgrades that don’t fall into classes 1-7. This includes locks and alarms that aren’t approved by Thatcham.


Does my car have a Thatcham alarm?

Almost all new cars in the UK are fitted with a Thatcham category 1 alarm but if your car is older, or second hand, it might not.

To find out for certain, you need to check your car owner manual or directly with the manufacturers. If you’re adding an alarm to your car, get one that’s Thatcham approved at the highest level to help drive down your insurance costs.


How do alarms, trackers and immobilisers impact my car insurance policy?

The higher the level of security you have, the more difficult your car is to steal. This means your car is safer and should go some way to giving you a lower car insurance price.

Making sure you have a Thatcham-approved alarm and car immobiliser could have a significant impact on your costs. If your car doesn’t come with these, you could install them.

Check with your individual insurer to see what impact it might have on prices.

Some insurers may specify that as part of a policy you need to have a tracker installed in your car. Failure to do this could make your policy invalid. Before taking out a policy it's worth checking the policy details to see if you do need to have one installed. 

If you want to beef up your security even more, consider keeping your car in a garage overnight. You can also take a look at our tips on lowering your car insurance costs.

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