You might've heard of car immobilisers before, but what are they? It's a pretty handy piece of technology that stops thieves stealing your car without the right key or fob. Having a car with an immobiliser fitted makes your car more secure and can help make your car insurance cheaper.
Key takeaways
- A car immobiliser is a handy device that stops the engine from starting without the correct key or signal. Even if a thief has physically broken into the car, it's not going anywhere
- All cars manufactured in the UK after 1998 are legally required to have a factory-fitted immobiliser
- Ever heard of a ghost immobiliser? They're aftermarket upgrades that use a unique PIN entered via the car's existing buttons. Because it has no wireless signal, it's immune to relay attacks
- Thatcham-approved security devices are the standard insurers recognise, and fitting one can lower your premium
- Be aware: If your immobiliser develops a fault, it can stop your own car from starting! So always check the battery and key fob first
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 thieves attempting to hotwire your car. Let's break it all down step by step:
When you get in your car, the key or fob sends an electronic code to your car's Electronic Control Unit (ECU). It sounds pretty confusing, but this code enables you to 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:
- Fuel system
- Starter motor
- Ignition
All you need to know is that 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?
Fortunately, there is a general rule of thumb that can help you figure out whether your car does. This largely 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.
Advantages of having a car immobiliser
In a couple of words? Greater security. Simply put, having a car immobiliser can reduce the chance of someone stealing your car. This is because an immobiliser makes it harder for a thief to hotwire your car and drive it away.
The good news is that, for the most part, 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.
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.
To help improve your car's security, you could also:
-
Install a wheel lock
-
Add an alarm
-
Put your fob in a faraday pouch
What is a ghost immobiliser?
Boo! Just kidding- it's not the scary variety. A ghost immobiliser is another type of device that you can fit discreetly into 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 or the steering wheel. There's no keypad involved, so it's pretty discreet, making 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.
Ghost immobilisers are always an aftermarket fitting. No car comes with one factory-installed.
The Autowatch Ghost Immobiliser isn't Thatcham approved, but that doesn't mean it's not effective. The Autowatch Ghost Immobiliser is a new generation of digital vehicle security that works differently to traditional alarms and trackers. This makes it difficult for Thatcham to assess, as it doesn't exist in their testing framework.
Because it isn't Thatcham approved, not all insurers will recognise the Autowatch Ghost Immobiliser.
When an insurer asks for a 'Thatcham-approved device', they are typically asking for a GPS tracking system, such as a Thatcham Category S7 or S5 tracker. Their primary goal is 'to recover stolen vehicles to minimise financial loss'. Because the Ghost is a pure immobiliser meant for theft prevention and lacks tracking capabilities, it may not meet this specific policy requirement on its own.
But while it isn't Thatcham approved, it's TASSA-accredited and widely recognised by insurers for its covert anti-theft technology. If you're unsure whether your insurer recognises the Autowatch Ghost Immobiliser as a legitimate security device, always double-check, as it can vary between providers.
The average car immobiliser cost varies, but you're typically looking at around £400 to £700 as the combined price for the device and installation.
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Common immobiliser problems
Faulty engine immobilisers are rare, but when it does happen, they could cause car problems.
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 thing to do is 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 3 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 frequently go off accidentally.
If you're wondering why your car alarm might keep going off, it could be down to manufacturing errors or even a low battery.
Silent alarm systems
These alarms 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 call 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 won't 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 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 S5 – 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 S7 – tracker
A Thatcham Category S7 replaced the older Category 6 and 7 standards. It provides essential, reactive stolen vehicle recovery features, global GPS tracking, and tamper alerts to satisfy basic insurance requirements.
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 secondhand, it might not.
To find out for certain, you need to check your car owner's 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 car insurance costs.
How do alarms, trackers and immobilisers impact my car insurance policy?
The greater level of security you have in place to protect your car, 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 £819
- If they have a factory-fitted immobiliser, the average cost comes down to £712
- Those with a Thatcham device pay £755, 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.
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*Median cost of car insurance. Confused.com data, April - June 2026.
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