A guide to immobilisers

An engine immobiliser allows your car to start only when the correct key or fob is used, protecting it against thieves.

Car security

25 January 2021

What is an immobiliser? All you need to know

As you might already know, adding extra security features to your car can help keep your insurance premium low. An engine immobiliser is one of the things you can add which may make a saving. Some people might not even know if their car has an immobiliser or not, which means they can end up paying more than they need to. Some of you might even be asking yourself ‘what is an immobiliser?’

What is an immobiliser?

An immobiliser is an electronic device that’s fitted into a car to stop the engine from running unless the correct key or key fob is present. Since the engine can only be started with the correct key, it means it can’t be hotwired, even if someone breaks into it.

Three main components make your car start – the ignition, the fuel system, and the starter motor. Mechanically speaking, an immobiliser works by disabling at least two of these three components. When any of these parts are disabled, the car can’t start.

Putting your key in the ignition will send a unique code from the key to the electronic control unit (ECU), which has the same unique code. So, using the wrong key/key fob - or no key at all - will make the immobiliser kick in as the codes won’t match.

Silver car parked on driveway in front of garage with a brown door

How to check if your car has an immobiliser

If you don’t know if your car has an immobiliser or not, there are a few notes that can help with that. To check if your car has a factory-fitted immobiliser, you can check your car’s handbook. This book should have all the details about your car, including whether or not it has an immobiliser fitted.

If your car is secondhand, it’s possible that a previous owner may have disabled or removed its immobiliser. There are several reasons why a previous owner might have done this, such as:

  • Faulty coding
  • Parts have been replaced in an area of the car where the immobiliser data is different
  • A previous owner lost their keys, and the new ones weren’t programmed properly
  • The car’s battery was replaced – all old key information is lost when this happens
  • An electrical surge in the car blew a component in the ECU

On the contrary to this, if your car is secondhand, a previous owner may have had a new or replacement immobiliser fitted. So, while it may not be factory-fitted, the car could still have an immobiliser.

All information relating to the immobiliser – including whether it has been removed or replaced - should be reflected in your car’s handbook. However, if this information isn’t clear, any qualified mechanic should be able to assess the car and confirm for you.

What is a Thatcham device?

Thatcham is an independent company that rates a car’s security to help insurance providers calculate your insurance premium. This independent evaluation looks at your car’s safety features, such as alarms and immobilisers. It’s important to note that Thatcham rates some alarms and immobilisers better than others.

You can find out your car’s rating on Thatcham’s website. You’ll be asked to enter details about your car, such as make and model, fuel type and year of manufacturing. You’ll then be given a series of results about your car’s safety, such as a theft rating, whiplash rating and group rating.

These results will determine how safe your car is and will be used to help your insurer determine a fair premium.

Will an immobiliser lower my car insurance premium?

Having an immobiliser will make your car significantly safer, which means it’s going to be harder to steal. This is a good thing, as it makes you less of a risk to car insurance providers and can result in you getting a fairer premium. A factory-fitted and Thatcham-approved immobiliser is the best option since it is the highest-rated. Be sure to always check with your insurer for their car insurance policies, as they will differ between suppliers.