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What is a car immobiliser?

November 18, 2022 by

Our guide details what car immobilisers are, and how they work

Immobilisers are electronic devices that prevent your car from being started with the incorrect key. This adds an extra layer of security to your vehicle and can help lower insurance premiums. Read on to find out more about how they work and whether your car has one fitted as standard.

What is an immobiliser?

An immobiliser is an anti-theft device that will only allow your car to start if it receives the correct code from the car key. This prevents thieves from being able to bypass your car’s ignition system and driving off with the vehicle.

Most modern immobilisers have a transponder embedded in the car’s key fob that transmits a code to the ECU whenever you insert the key into the ignition barrel. Early immobilisers sometimes used a separate fob or required a button to be pressed inside the vehicle to deactivate the immobiliser. Some cars had a keypad which could be programmed to accept a four-digit number before the car would start.

Modern cars have immobilisers built into their keys

Vehicles with keyless entry and start functions require the key to be within close proximity of the car. Some cars even allow you to use your smartphone as a key, in this case the code is transmitted from the phone to the car’s ECU.

In early immobiliser units, just one code was programmed into the system. Modern immobilisers will use a different code each time you start the car.

How do immobilisers work?

The main purpose of the immobiliser is to prevent an unauthorised person from driving off with the car. It does this by controlling the starter motor, fuel system and ignition system.

Even if the correct key is used, if the immobiliser does not receive the right code it will not activate one or more of the abovementioned systems.

If the ignition system is ‘hotwired’ or bypassed, the immobiliser will still prevent the car from starting as the fuel system and/or starter motor will not respond.

Does my car have an immobiliser?

It has been mandatory since 1998 for all cars to have a factory-fitted immobiliser, however, your car may still have one fitted even if it is older than that.

That’s because the first automotive immobilisers that used a key with an embedded transponder arrived in 1992 and many luxury automakers incorporated them into their vehicles soon after.
Some auto manufacturers like BMW had rudimentary immobilisers of their own even before 1992. Most in the form of keypads which would require the correct code to be input before the car would respond to the ignition key.

If your car was built before 1998 and you are unsure of whether it has an immobiliser, check the owner’s manual or contact the manufacturer to find out. It may also have been fitted with an aftermarket immobiliser.

What are the different types of immobiliser?

While it is required by law for every new car to have an immobiliser, not all systems are equal. Factory-fitted immobilisers are well integrated into the vehicle’s electronics and should work perfectly every time. However, technology is constantly evolving, and some older immobilisers may become vulnerable to hacking.

If you are looking to upgrade your immobiliser or don’t have a factory-fitted unit, there are several aftermarket options available to you.

Some offer WiFi connectivity, undetectable installation, pin code entry via dashboard buttons and many other features. To make sense of it all, the Thatcham Research organisation has developed a grading and approval system for anti-theft devices.

Immobilisers help prevent car theft

Thatcham Research was founded in 1969 to help contain motor insurance costs without compromising safety standards. Since then, it has been testing, researching and evaluating vehicle safety and security to provide an unbiased assessment of automotive technologies.

Thatcham provides a security certification for every immobiliser and alarm system it tests. This provides added reassurance around how the safety systems perform, and it is why you should only purchase a security device for your car that has been through their stringent testing process.

Thatcham has divided car security into seven different categories. There is also a Q category for aftermarket systems that do not fall into the standard ratings categories.

Category 1 – Electronic alarm and immobiliser

The alarm system in category 1 vehicles will need to have perimeter detection and sensors to detect vehicle movement. The immobiliser has to be able to control at least two vehicle operating systems.

Category 2 – Electronic immobiliser
This category is for cars with electronic immobilisers. They must also be able to control two vehicle critical functions at a minimum.

Category 2/1 – Electronic alarm upgrade
This category is for a car that has had an aftermarket alarm fitted when one was not present when new. This is usually done to increase security and potentially reduce insurance premiums. The alarm needs to meet the same criteria that apply to category 1 alarm systems.

Category 3 – Mechanical Immobiliser
This category is for cars fitted with mechanical devices like a steering wheel lock or wheel clamp. These devices need to be fitted every time the vehicle is left unattended.

Category 4 – Wheel Locks

This is for wheel locking devices such as wheel nuts that require a unique tool to remove. This makes them more difficult to steal and also serve as a visual deterrent.

Category S5 – Post-theft tracking

This category is for systems that track a vehicle’s location if it is stolen. They also enable vehicle remote immobilisation, can alert the police or a security company and also feature driver identification, usually in the form of a small tag which the car will not start without.

Category S7 – Stolen vehicle location

This is similar to the S5 rating but does not feature driver recognition technology and does not allow for the car to be immobilised remotely.

Q Class – Non-categorised aftermarket devices

These are vehicle safety devices that have not been approved by Thatcham.

If I’ve got an older car, should I get an immobiliser fitted?

There is no doubt that immobilisers have helped lower vehicle theft since they were introduced. While individual studies vary on exactly how effective they are, on average it has been estimated that car theft has been reduced by 40% due to immobiliser technology.

So, if you have an older car that does not have an immobiliser, then it’s definitely a good idea to have one fitted. Costs for the system and installation vary between £200 and £500, with some companies offering on-site fitment. Remember to only use Thatcham approved devices.

While most insurance company premiums already account for an immobiliser in newer vehicles, you may save on your monthly payments if you have one installed in a vehicle that did not come with one as standard.

What happens if my car’s immobiliser breaks?

A malfunctioning immobiliser is quite rare, especially if it is a factory-fitted unit. However, as with any electrical component it can fail or cause intermittent issues.
Here are the signs to look out for:

  • Car won’t lock or unlock properly
  • Engine won’t start
  • Alarm keeps going off unexpectedly

The good news is that in the majority of cases the problem can be traced to a dead or dying key fob battery. Depending on the make and model of your car, a battery replacement can be a simple DIY job or require a visit to the dealer. Check the owner’s manual to see what you need to do.

If a key fob battery replacement doesn’t solve your issues, then there might be wiring or other electrical issues causing the problem. In this case you should contact your dealership or mechanic.

Can car thieves beat an immobiliser?

Immobilisers have been instrumental in reducing car theft, but they aren’t fool proof and there’s still a chance that your car could be stolen. The methods used range from the rather basic but effective method of towing your car away to wireless relay transponders that clone your key’s unique code.

In fact, with many modern cars coming standard with keyless entry, keyless car theft is on the rise and responsible for a significant portion of the 100,000+ cars that are stolen in the UK each year. Some manufacturers allow you to disable the keyless entry function, or you could even place your key in a Faraday bag which will prevent the signal from being intercepted.

What other ways can I immobilise my car?

Your best defence against car thieves is to have a multi-level approach to your car’s security. A combination of electronic and physical security devices will help deter both the more technologically adept thieves as well as ones trawling your neighbourhood in a flatbed truck.

Electronic Devices

  • Alarm systems
  • Car trackers
  • Remote immobilisation
  • Driver identification

If a thief manages to gain access to your vehicle, an alarm or driver identification device will prevent them from getting any further. If they do manage to drive away, you will want to have the ability to track and remotely disable your car.

Physical Devices

  • Steering wheel locks
  • Wheel Clamps
  • Gear Locks

Having a great big steering lock or wheel clamp on your car can visually deter criminals and can’t be bypassed by fancy electronic devices.

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