Keyless Car Theft: How Relay Attacks Work and How to Stop Them
If your car unlocks when you walk up to it with the key in your pocket, it can be stolen in under a minute without the thieves ever touching your key. This is how the attack works, how to tell if your car is at risk, and what actually stops it.
The short version. Thieves relay the signal from your key through the wall of your house to your car on the driveway. Anything that blocks the signal — a Faraday pouch, a metal tin — stops it. Distance from the front door helps too.
How a relay attack works
A keyless fob is not asleep. It listens constantly for a low-power signal from the car, and when it hears one it answers, and the car unlocks and starts.
A relay attack uses two people and two devices. One stands by your front door with a receiver and picks up the faint signal from your key, which is usually on a hook in the hall or in a bowl by the door. That device sends the signal to a second device held next to your car. Your car hears what it thinks is your key standing right beside it, unlocks, and lets the engine start.
No window is broken, no alarm goes off, and nothing on the car is damaged. People often find out when the driveway is simply empty in the morning.
Is your car at risk?
If you can unlock the doors without pressing a button on the fob, and start the engine with a button rather than turning a key, your car uses keyless entry and is in scope. Most cars sold in the last decade with push-button start are.
If you have to press a button on the fob to unlock, you are at much lower risk from this particular attack.
What a Faraday pouch does
A Faraday pouch is a small bag lined with a conductive metal mesh. Put the key inside and close it properly, and the mesh blocks the radio signal in both directions. The relay device at your front door hears nothing, so there is nothing to relay.
It is the cheapest fix there is, it needs no fitting, and it works on any fob.
Test yours when it arrives
Do not assume. Put the key inside, close the flap fully, walk up to the car with the pouch in your hand and try the door handle. If the car unlocks, the pouch is not sealing — usually because the flap is not folded over far enough, or the lining is worn. A pouch is a consumable: check it every few months, because the mesh does tire with use.
Five other things that help
- Move the keys away from the front of the house. The relay only works at short range. A drawer in a back room is harder to reach than a hook in the hall.
- Keep the spare in a pouch too. Thieves do not care which key answers. The spare in the kitchen drawer is just as useful to them.
- Turn on motion sleep if your car has it. Many makers now ship fobs that go dormant after a few minutes of stillness. Check the handbook — it is often off by default.
- Add something visible. A steering wheel lock is old-fashioned and that is the point: it takes time and it is obvious from the pavement.
- Park defensively. Nose-in on a driveway, or boxed in behind another car, makes a quiet getaway much harder.
A pouch blocks the relay attack. It does not stop every kind of car theft — key cloning through the OBD port and plain towing still exist — but relay theft is the common one, and it is the one that costs least to prevent.
What to look for in a pouch
- A double lining. Two layers of mesh block more reliably than one.
- A deep flap. The seal is where cheap pouches fail. The flap should fold well over the opening.
- Big enough for your fob. Modern fobs with a display are larger than you think.
- Buy a pair. One for the main key, one for the spare.
If your car is stolen, report it to the police on 101 and tell your insurer the same day. If you have a tracker, call the tracking company first — the first hour matters most.
Common questions
How do I know if my car is at risk of relay theft?
If you can unlock the doors without pressing a button on the fob, and start the engine with a button rather than a key, your car uses keyless entry and is in scope.
Does a Faraday pouch really work?
Yes, when it seals properly. Test it: put the key in, close the flap fully, walk up to the car and try the handle. If the car unlocks, the pouch is not sealing.
Will kitchen foil work instead?
Foil can block the signal, but it tears, it unwraps in a pocket and there is no way to tell when it has failed. A lined pouch is a few pounds and far more reliable.
Does a pouch stop every kind of car theft?
No. It stops relay attacks, which are the common method against keyless cars. Key cloning through the OBD port and plain towing still exist, which is why a visible steering lock is worth adding.