The immobilizer: Protection against car thieves

The increasing number of car thefts in the early 1990s led to the Road Traffic Licensing Regulations (StVZO) being changed with effect from January 1, 1998, so that all vehicles newly registered in The United Kingdom must have an electronic immobilizer. Even if this still does not offer 100% security, it can be clearly seen that this regulation has had its effect if you take a closer look at the statistics of car thefts. While more than 105,000 cars were stolen in 1993, in 2003 there were still around 31,700 and in 2013 only around 18,800 vehicles. However, immobilizers are not only used to prevent a car from being stolen. The police and public order office also use mechanical immobilizers when they have to pull a vehicle out of traffic. In this article you will learn how this car anti-theft system works, the different types there are, how you can unlock a mechanical and an electronic immobilizer and what you can do if your car does not start due to a defect.

What is an electronic immobilizer and how does it work?

This type of anti-theft device is designed to prevent your vehicle from being started without the associated key. Most of the time, however, you don't even notice that your car has an immobilizer, because you activate it automatically when you switch off the engine and deactivate it again when you start it. But how exactly does that work?

 In general, a distinction can be made between the following three generations: 

  1. Three Circuit Breaker: This first generation was installed in the 1990s as a car anti-theft device. This prevents the engine from starting by interrupting the connection between the fuel supply, ignition and starter. Today, however, it is no longer used because it can be cracked relatively easily, since only an electrical switch has to be bridged.
  2. Radio-frequency identification (RFID): This second generation immobilizer was introduced in the mid-1990s and ensures that the engine control unit is blocked. Activation and deactivation takes place via an electrical impulse that is sent to the engine control unit by an RFID chip integrated in the car key. However, this only works with the key that matches the vehicle, as the chip it contains has a specific serial number that is queried by the control unit, which is only unlocked if there is a match.
  3. Optimized magnetic frequency identification: As professional vehicle thieves are also constantly evolving and at some point have found ways to interrupt the signal between the key and the control unit, the second generation has been optimized in the third. This optimization consists in encrypting the signal sent by the RFID chip.

Although an electronic immobilizer in the car cannot completely rule out theft, it still makes sense, since opportunistic thieves in particular are unable to crack it. Even professional thieves are slowed down by this anti-theft device at least long enough for the risk of being caught to increase sharply. If you want to protect your car even more against unauthorized access by third parties, you have the option of installing a car alarm system or using an additional mechanical immobilizer.

How does an electronic one differ? from a mechanical immobilizer?

In contrast to the electronic immobilizer, mechanical vehicle anti-theft protection is not mandatory, but can be used voluntarily as additional protection. In addition, this is particularly popular with law enforcement officers in the form of wheel claws and valve guards.

  • Wheel clamp: This can be attached to the rim of any wheel and is secured with a lock. Due to the locked wheel, it is no longer possible to drive the vehicle.
  • Valve guard: This is screwed onto the valve of a vehicle tire and ensures that the valve is opened at a speed of more than 15 km/h, which means that the air escapes from the tyre. However, this immobilizer is heavily criticized because it is still possible to drive the vehicle at walking speed, it can be circumvented by changing a tire and it is often not noticed, which means that the flat tire it causes can quickly lead to an accident with injuries .
  • Steering wheel claw: This cuts in Mechanical immobilizer tests always do very well because it has a good deterrent effect and is cheap and reliable. The steering wheel claw is attached to the steering wheel and a pedal, which effectively prevents both the movement of the steering wheel and the operation of the pedal.
  • OBD saver: This is attached to the OBD socket and blocks access to the on-board computer, which prevents car thieves from using a laptop, for example, to access the vehicle controls and deactivate the electronic immobilizer.
  • Gear shift lock: This is installed in the center console and secured with screws. It blocks the shift in reverse gear or in the P position in automatic transmissions.

Which cars have an immobilizer?

According to Section 38a, Paragraph 1 of the Road Traffic Licensing Regulations, vehicle manufacturers have been obliged since 1998 to equip all passenger cars, trucks, tractor units and tractor units with a maximum permissible total weight of 3.5 tons with an electronic immobilizer. Heavier vehicles are exempt from this obligation as they are less likely to be stolen due to their size. Even mopeds, trikes, bicycles with an auxiliary motor as well as agricultural and forestry machines do not necessarily need an electronic immobilizer. However, these can be optionally provided with mechanical anti-theft protection. For motorized two- and three-wheelers that have a maximum speed of over 45 km/h and a displacement of more than 50 cubic centimetres, another security device, such as a lock, is mandatory to prevent theft. Nowadays, however, electronic immobilizers are already installed as standard in most motorcycles.

Although you as the vehicle owner are not obliged to retrofit such anti-theft protection, you should still make sure that your vehicle is equipped with it and that it works. This is especially true when buying a used car. Because if your car is stolen because it has no or a defective immobilizer, your insurance may not pay for the theft at all or only partially.

What if the immobilizer is defective is?

However, it can also happen that you as the vehicle owner can suddenly no longer start your car despite having the right key, or that the immobilizer symbol lights up on the dashboard. The cause of this can either be a dead car battery, a dead battery in the car key or defective wiring. If the battery is dead and you change it in good time, you can then start your vehicle normally again without any further action being required. 

However, if changing the car battery or changing the battery of the car key too late results in the data on the RFID chip being deleted, unfortunately a trip to the car workshop is unavoidable. In this case, the chip must first be reprogrammed to your vehicle. The car mechanics can also determine whether the cause was actually just a dead battery or whether there is even another defect. In the latter case, the defective component must be replaced and the transponder reprogrammed. 

Incidentally, this is also necessary if you lose your car key or the engine control unit needs to be replaced. If you completely deactivate the electronic immobilizer instead, you not only risk your full insurance cover but also a warning fee of 10 euros.


The introduction of the obligation to install an electronic immobilizer has led to a drastic reduction in reported car thefts, but these can still not be completely ruled out, since professional car thieves are also constantly evolving. To reduce the risk even further, you should always make sure that you always remove your car key even for short stops, always carry the key with you when you travel, do not leave a spare key in the car, always lock the steering wheel when parking and all to close the windows and possibly the sunroof.

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