Car immobilisers explained

All modern cars should have an immobiliser fitted as standard. It's a key piece of technology to stop thieves stealing your car. And if you don't have one, you can have one fitted.

Having a car with an immobiliser fitted makes your car more secure, which in turn should help to make your car insurance cheaper. Here's what you need to know.

What is a car immobiliser?

A car immobiliser is an anti-theft device that only lets your car start if you’re using the correct key or fob. This means your car is protected against hotwiring from thieves. Here's how it works:

When you get in your car, the key or fob sends an electronic code to your car's Electronic Control Unit (ECU). This code lets you start your car.

If a thief tries to use anything other than the correct key, the car shouldn’t work. The ECU should detect that the wrong electronic code - or no code at all - is being used. The car's immobiliser then disables 2 of 3 important components:

• The fuel system
• The starter motor
• The ignition

This means the thief can't make the car move. Insurers generally consider a factory-fitted device to be the best type of car immobiliser. These have been installed by the manufacturer, so they're more likely to function properly.

Does my car have an immobiliser?

It depends on how old your car is:

• If your car was built after October 1998, you should have a factory-fitted immobiliser
• If your car was built before October 1998, you might not have one

The best way to check is to look at your owner’s handbook. Most manufacturers have these online so you can download a digital copy and search for the word 'immobiliser'.

If you can't find any information in your handbook, contact the manufacturer or ask a qualified mechanic to check for you.

What are the advantages of having a car immobiliser?

The main advantage of having a car immobiliser is that it it reduces the chances of someone stealing your car. This is because an immobiliser makes it harder for a thief to hotwire your car and drive it way. And our data shows that the average theft claim is over £14,000*, so improving your car security should be a priority.

This increased security also helps you get lower car insurance prices.

It's not a total security system though. Determined thieves could still tow your car away. And an immobiliser doesn't stop thieves breaking into your car to steal your valuables.

What is a ghost immobiliser?

A ghost immobiliser is another type of device that you can fit discreetly to your car. It offers an additional layer of security.

To start the car, the driver has to enter a PIN using the buttons on the dashboard. This should make it significantly more difficult for thieves to steal your car.

You may be able to get cheaper car insurance with a ghost immobiliser, but check with your insurer first. You might need to fit an insurance-approved ghost immobiliser to get a discount.

How do car immobilisers impact my car insurance policy?

The higher the level of security you have, the more difficult your car is to steal. This should mean you pay less for your car insurance. When you compare car insurance quotes with us, we'll ask you "Does the car have an alarm or immobiliser?". Your options will be:

• Yes - Manufacturer fitted
• Yes - Thatcham device
• Yes - Other alarm or immobiliser
• No security device

According to our data*:

• The average car insurance cost for someone who has no immobiliser is £801
• If they have a factory fitted immobiliser, the average cost comes down to £695
• Those with a Thatcham device pay £751, on average

So even if you don't have a factory-fitted immobiliser, installing one that's approved by Thatcham could still help reduce your insurance costs. Check with your individual insurer to find out if it could reduce the cost of your car insurance.

If you're looking for more ways to save, read our guide on how to get cheaper car insurance.

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 you could get more of an insurance discount too.

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. This is as close to Class 1 as you can 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 alloy wheels, 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 simpler 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.

*Confused.com data. October 2022 - September 2023.