Immobiliser

An immobiliser or immobilizer is an electronic device fitted to an automobile which prevents the engine from running unless the correct key is there. This prevents the car from being "hot wired" after entrance has been achieved.

Immobilisers have been mandatory in all new cars sold in the UK since October 1998 and in Australia since 2001. In Canada, immobilisers are required in all cars assembled on or after 1st September 2007. Early models used a static code in the ignition key (or key fob) which was recognized by an RFID loop around the lock barrel and check against the vehicle ECU for a match. If the code is unrecognized, the ECU will not allow fuel to flow and ignition to occur. Later models use rolling codes or well developed cryptography to defeat copying of the code from the key or ECU.

The microcircuit inside the key is activated by a small electromagnetic field which induces current to flow within the key body, which in turn broadcasts a unique binary code which is read by the automobile's ECU. When ECU determines that the coded key is both current and valid, the ECU activates the fuel-injection sequence.

In some vehicles, attempts to use an unauthorized or "non-sequenced" key cause the vehicle to activate a timed no-start condition and in some well advanced systems, even use satellite or mobile phone communication to alert a security firm that an unauthorized attempt was made to code a key.

Coincidentally, this information is often recorded in modern automobile ECUs, which may record lots of other variables including speed, temperature, driver weight, geographic location, throttle position and yaw angle. This information can be used during insurance investigations, technical troubleshooting or warranty claims.

Add-on immobilisers are presented for older cars or vehicles without factory immobilisers. The insurance approval for self-arming immobiliser is known as "Thatcham 2" after the Motor Insurance Repair Research Centre in Thatcham, Berkshire, England. Approved immobilisers must intercept at least two circuits; classically the low-voltage ignition circuit and the fuel pump circuit. A few may also intercept the low-current starter motor circuit from the key switch to the relay.

Statistics in Australia show that three out of four vehicle thefts are older cars stolen for joyriding, transport or to commit another crime. Immobilisers are built-in to around 45% of all cars in Australia, but account for only 7% of those cars that are stolen. In lots of instances, where a vehicle fitted with an immobiliser has been stolen, the thief had access to the original key. Only around one in four vehicles are stolen by professional thieves. The majority of vehicles are stolen by opportunistic thieves relying on finding older vehicles that have unsuccessful security or none at all.

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