What is a car immobilizer system and how does it actually work?

Question

What is a car immobilizer system and how does it actually work?

Answer 1

It makes it much harder for people to steal your car. The car immobilizer will refuse to start the engine unless a key is detected. If a robber wants to rob something, he'll do it, but the cars that have an immobilizer are much much much harder to start without a key  

Answer 2

The Immobilizer prevents the car from running unless an authorized key is present and has been properly matched to various components in the vehicle.

Several different Immobilizer schemes have been used for different years and different models of vehicles with different procedures that apply to them.

The components of the Immobilizer system that require special procedures for replacement include the keys, Engine controller (ECU), and the Instrument Cluster (or the separate Immobilizer modules in vehicles so equipped).