Immobilizer
A factory immobilizer checks a coded chip in the key before the engine will run. A copy of the physical key without the chip will not start the car.
Starter interrupt
A starter interrupt is added by an alarm. It cuts a circuit the starter needs while the alarm is armed. Even if the ignition is defeated, the engine will not crank.
Why both help
They defend against different tricks. The immobilizer fights key copying. The interrupt fights bypassing the ignition. A vehicle with neither is the easiest target.
How they work together
The immobilizer says "this key is allowed." The starter interrupt says "and nobody has told me to stay quiet." If either one says no, the engine does not run. Two simple checks are harder to get around than one.
Quick answers
Does my car have an immobilizer?
Check your manual or ask your dealer. Many older models do not.
Can a starter interrupt be bypassed?
It adds a barrier, not an absolute.
