An immobiliser is an anti-theft mechanism that prevents an automobile's engine from starting unless the correct ignition key or other device is present. This device prevents thieves from starting the car by a method known as hot wiring. Most new vehicles have an immobiliser as standard equipment. An important advantage of this system is that it doesn't require the car owner to activate it; it operates automatically. An immobiliser is considered as providing much more effective anti-theft protection than an audible alarm alone; many auto insurance companies offer lower rates for vehicles that are equipped with them.
As an anti-theft device, an immobiliser disables one of the systems needed to start a car's engine, usually the fuel supply or the ignition. This is accomplished by radio frequency identification between a transponder in the ignition key and a device called a radio frequency reader in the steering column. When the key is placed in the ignition, the transponder sends a signal with a unique identification code to the reader, which relays it to a receiver in the vehicle's computer control module. If the code is correct, the computer allows the fuel supply and ignition systems to operate and start the car. If the code is incorrect or absent, the computer disables the system, and the car will be unable to start until the correct key is placed in the ignition.
By disabling the ignition electronically through the computer, an immobiliser prevents the vehicle from being stolen in most cases. The most common way a thief starts a car's engine is by hot wiring. This involves breaking the steering column open and connecting the ignition wires by hand rather than turning a key to connect them. When the ignition systems are disabled by the car's computer, this theft method doesn't work; even with the wires connected, the car still won't start. Immobilisers are so effective at preventing theft that they are now offered standard on most new cars; they can also be installed as an aftermarket option on older vehicles.
One of the most important advantages of an immobiliser system is that the car owner does not have to remember to activate it; its operation is automatic. An immobiliser provides more effective protection against theft than an audible alarm which provide less protection when used alone. The device is considered a passive anti-theft system since it doesn't require action from a person to make it work; it also often qualifies a vehicle for a discount or lower rates on auto insurance. One disadvantage of the system is that car keys with the embedded transponder are more expensive and time consuming to replace if lost and usually requires a visit to a car dealer.