A Quick Guide to Your Car Immobiliser

A recent poll found that cars rank highly in the list of prized possessions Brits would hate to lose (eighth for women and third for men). If you feel the same way, a car immobiliser could go some way towards keeping your pride and joy safe. 

So, what is an immobiliser on a car? How does it work? How do you know if your vehicle already has one? And do engine immobilisers make your car insurance cheaper?

We answer all these questions (and more) below.

What is a car immobiliser?

A car immobiliser is a type of electronic security device. 

It prevents a vehicle’s engine from starting unless the correct key or fob is used. It also stops vehicles from being hot-wired, a technique used by thieves to bypass the ignition and start the engine.

Factory-fitted immobilisers are generally considered the best option. That’s because they’re installed by the manufacturer and are more likely to work correctly. 

Since October 1998, all new vehicles in England and Wales must have an immobiliser fitted as standard. If your car is older than this (or you imported it from a country where immobilisers weren’t mandatory), you can always have one installed by a qualified mechanic.

How do car immobilisers work?

Most immobilisers stop the starter motor, ignition system, or fuel system working until the right key or fob starts the car. Sometimes the immobiliser shuts off all three until that happens.

The key or fob in question will contain a tiny computer chip coded specifically to your vehicle. When you use it to start your car, it’ll send a code to your car’s Electronic Control Unit (ECU). The immobiliser detects the matching code and switches itself off, and the engine starts. 

Think of it like using a password to gain access to your vehicle. If someone tries to start your car using a different key or fob, the code sent to the ECU won’t match. That means the car won’t start.

And in some modern vehicles, the wrong code acts as a red flag. If one is detected, the car alarm will sound to draw attention to a possible theft. 

How do I know if my car has an immobiliser?

If your car was made after 1998, it should have an immobiliser installed. 

If your car is older, or you bought it second hand, it’s a good idea to double-check if it has one. Some cars made before 1998 still had immobilisers fitted, while others may have had them installed later.

First, flick through your owner’s manual. That should tell you if your vehicle had a factory-installed immobiliser. Otherwise, contact the manufacturer, or ask a qualified mechanic to check for you.

Do car immobilisers prevent theft?

Will your car immobiliser prevent a thief stealing your vehicle?

Immobilisers are pretty effective at deterring car thieves. One study found they reduced theft by an estimated 40%.

However, they aren’t perfect. An immobiliser might make your car harder to steal, but it’s not impossible. Savvy car thieves have sussed out how to get around these systems, with keyless car theft on the rise. 

This is when a thief uses a relay-style electronic device to redirect your key fob signal. Their device then assumes all key fob power, allowing them to open your car and start the ignition. This YouTube video shows one of these devices in action. Gone in 60 seconds. 

And if thieves can’t crack your immobiliser’s code, they could still tow your car away and work on it elsewhere.  

For extra peace of mind, consider adding a few additional layers of security. For example, you could install a steering wheel lock, a silent alarm, or a GPS tracker to deter thieves further.

Steering wheel locks do what they say on the tin. They lock the steering wheel in place, acting as a visual deterrent to would-be car thieves.Silent alarms go off when someone tries to break into your car. But as the name suggests, they don’t make a sound. Instead, you’ll get a separate alert, usually via a connected smartphone app. This gives you the chance to call the police and let them know your vehicle is being stolen. Don’t try to take matters into your own hands—confronting a car thief could be dangerous. A GPS tracker won’t stop a theft from happening, but it could help you find your vehicle later. Many of the trackers available on the market will show you where your car is in real time on a connected smartphone app. Again, it’s a good idea to involve the police rather than deal with it yourself. 

Note: If your car has keyless entry, it’s a good idea to keep the fob away from the front door or in a faraday bag (a sealed bag that stops electrical signals from being sent and received).

How much does it cost to fix a car immobiliser?

Problems with car immobilisers are relatively uncommon, but they can happen. If your immobiliser stops working, you might find it tricky to:

Lock and unlock your carStart your engineArm or disarm your alarm

Before you take your car back to the dealership or to a garage, try changing the battery in your fob. That’ll often do the trick. If it doesn’t, you’ll need to speak to a qualified mechanic familiar with your car’s make and model. 

According to WhoCanFixMyCar.com, the average cost of fixing a faulty immobiliser is £100.

Does having a car immobiliser affect insurance rates?

Car immobilisers help improve vehicle security and lower the risk of theft. And generally speaking, the safer your car, the lower your car insurance price.

However, not all car security devices are created equal. That’s why most insurers will look at the Thatcham rating of your vehicle before calculating the cost of your insurance. 

What is a Thatcham-approved alarm (and does my car have one?)

Thatcham is an independent vehicle research company. Since the 1990s, they’ve been assessing alarms and immobilisers. And they’ve developed seven categories for car security that have  become the industry benchmark for manufacturers and insurers. 

Let’s take a look at the different categories. Remember, the closer your vehicle is to category 1, the more secure it is—meaning potentially lower car insurance costs. 

Thatcham RatingMeaningCategory 1: Electronic Alarm and ImmobiliserThese are the smartest, most complex devices on the market. The alarm should have its own battery supply, while the immobilisers should disable two of the three systems required to drive the car. It should also be passively set (without any action required from the driver). Category 2: Electronic ImmobiliserThis is essentially a category 1 immobiliser without the alarm. Just like the category 1 rating, the immobiliser must disable two of the three operating systems and be passively set.Category 2/1: Alarm UpgradeIf your car is in category 2, you can upgrade it to this category by retrofitting a category 1 alarm. It won’t give your vehicle category 1 status, but it’s as close as you’ll get without buying a new car. Category 3: Mechanical ImmobiliserThis covers mechanical devices that need to be manually set each time, as opposed to the electrical immobilisers described above. They need to isolate at least one operating system required to drive the car. These devices include steering wheel and gear lever locks.Category 4: Wheel Locking DevicesIf your car has alloy wheels, it will probably have locking wheel nuts. This means they can only be removed with a special key, making your wheels harder to steal.Category S5: Post-Theft Tracking & RecoveryPreviously the Thatcham category 5, the new S5 category covers systems that can track the location of a stolen vehicle and remotely immobilise it. Category S7: Stolen Vehicle LocationThe S7 category replaced the previous category 6 and category 7 ratings. Similar to S5, S7 covers tracking, but doesn’t include remote immobilisation. 

Almost all new cars in the UK are fitted with a Thatcham category 1 alarm and immobiliser.

However, older cars may not have one. If you’re unsure, check your owner manual or contact the manufacturer. And if you’re planning on adding an alarm to your car, make sure it’s Thatcham-approved at the highest level. Doing so could help you save on your insurance premium.

Quickfire summary:

Car immobilisers are a crucial part of overall vehicle security, helping to deter thieves and reduce rates of car theft. 

To keep your car safe (and your insurance premiums lower) make sure your car has a category 1 Thatcham-approved alarm and immobiliser. If it doesn’t, you can always get one installed by a qualified mechanic. 

Also read:
Cars most likely to be targeted by thieves
Where is your car most likely to be stolen?
Protect your keyless vehicles from theft
Where should you park your vehicle at night?