Keyless Car Theft: How Relay Attacks Work and How To Stop Them

Keyless entry is convenient, and that convenience is exactly what thieves exploit. If your car unlocks when the key is in your pocket, it will also unlock when the key is on a hall table and someone is standing outside your front door with the right equipment.

How a relay attack works

Your keyless fob is constantly listening for a low-frequency wake-up signal from the car. A relay attack uses two devices and two people. One stands close to your house, capturing the fob's response through the wall; the other stands by the car, retransmitting it. The car believes the key is next to the door handle, unlocks, and allows the engine to start. The whole process takes under a minute and is silent.

Signal jamming

A cruder variant: the thief transmits noise on the fob's frequency as you walk away and press lock. The car never receives the lock command, you hear no confirmation because you are already walking, and the car is left open. Always look for the indicator flash or listen for the lock confirmation before leaving.

CAN injection

The newest method skips the key entirely. Thieves access wiring behind a headlight or wing mirror and inject messages onto the vehicle's CAN bus that tell the immobiliser a valid key is present. It requires physical access and specialist hardware but has been documented against several popular models.

What actually works

1. **A signal-blocking pouch (Faraday pouch)** — a few pounds, and it defeats relay attacks completely as long as you use it every single time, including at home. Test it: put the key in, walk to the car, confirm the car does not respond.

2. **Motion-sensing keys** — many manufacturers since roughly 2019 fit fobs that go to sleep after a few minutes of stillness. Check your handbook; some models have this disabled by default and it can be switched on.

3. **A visible mechanical lock** — a steering wheel or pedal lock does not stop the electronics, but it makes your car the harder target on the street, and most opportunistic thieves move on.

4. **An OBD port lock or shield** — blocks the diagnostic port route used to programme a fresh key inside the car.

5. **A Thatcham-approved tracker** — does not prevent theft but sharply increases recovery rates and can reduce your insurance premium.

6. **Park defensively** — nose-in on a driveway, wheels turned, under a light or camera, and never leave the key by the front door or a window.

Where an auto locksmith fits in

We can delete lost or stolen keys from your immobiliser so they no longer start the car, supply and program replacement keys, and fit aftermarket immobilisers and OBD port protection. If you have bought a used car and cannot account for every key that was ever paired to it, deleting the unknown keys is a sensible first-week job.

Call +44 7347 492822 to discuss key deletion or security upgrades across West London and the Thames Valley.