A car immobiliser disables one of the systems needed to start a car's engine, usually the fuel supply or the ignition. This is accomplished by RF identification between a transponder in the ignition key and a device called a RF reader in the steering column. 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.
A car immobiliser is an anti-theft mechanism that prevents an automobile's engine from starting unless the correct ignition key (or Key FOB) is inserted into the ignition slot. One of the advantages of an immobiliser system is that the car owner does not have to remember to activate it - its operation is automatic. The device is considered as a passive anti-theft system since it does not require action from a person to make it work. 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. Most new vehicles have an immobiliser as standard equipment, but aftermarket or add-on immobilisers are available for older cars or vehicles without factory-installed immobilisers.