Signal Jammers: Why Your Car Might Not Be Locking
You press the fob, glance back, and walk off. But did the car actually lock? Signal jamming is one of the simplest and most common tricks thieves use — and most owners never notice it happening.
What a signal jammer does
A jammer is a cheap device that floods your key fob's radio frequency with noise. When you press ‘lock’, the car never receives the command — so it stays unlocked.
You see the fob press, assume it worked, and walk away. The thief strolls up to an open car.
Why it's so common
Jammers cost very little, need no skill and leave no damage. They're used in car parks, service stations, supermarkets and on driveways — anywhere a thief can sit and wait for you to walk away from the car.
How to spot it and protect yourself
- Always check the car physically locked — pull a door handle before you walk off.
- Watch for the indicators flashing and listen for the clunk of the locks.
- If the fob suddenly ‘won't work’ near your car, be suspicious — move the car and try again.
Good habits stop the opportunist grab from an unlocked car. But jamming only gets a thief in.
Stopping them driving away
Getting into a car isn't the same as driving it off. IMMOSTOP holds the engine immobilised at two separate points until your authorised phone is in range. A jammer can keep your car from locking — it can do nothing to release an IMMOSTOP cut point, so the car simply won't drive for anyone but you.
A jammer can stop your car locking. It can't start your engine. See how IMMOSTOP keeps it put →
Common questions
How do I know if my car was jammed?
The tell-tale sign is the fob appearing not to work right next to the car, or the car being found unlocked when you're sure you locked it. Always physically try a door handle before walking away.
Does locking the car manually help?
Yes — manually checking the doors defeats the ‘walk away from an unlocked car’ trick. But it won't stop a determined thief who gets in another way, which is why an immobiliser matters too.
Can a thief drive off after jamming my car?
Only if they can also start it. With IMMOSTOP fitted, the engine stays immobilised until your phone is present, so a jammed, unlocked car still can't be driven away.