What is relay theft, and how do thieves steal keyless cars?
Relay theft exploits the fact that a keyless entry system only checks whether the key is nearby — and thieves can make the car believe it is, by extending the signal.
How keyless entry works. The car continuously transmits a low-power signal. When the key fob comes within range, it responds with a cryptographically signed reply, and the car unlocks and permits starting. The cryptography is not broken in this attack — which is the crucial and frequently misunderstood point.
The relay attack. Two people with equipment:
One stands near the house, close to where the key is kept — a hallway table, a hook by the door — with a device that picks up the car's signal, relayed to them, and amplifies it to reach the key.
The key responds normally, believing the car is adjacent.
The second device, at the car, relays the key's genuine response back.
The car unlocks and starts. The whole operation takes under a minute and is silent.
What is actually being defeated is the assumption that signal range equals physical proximity. The messages are legitimate; only the distance is faked.
Other methods in use:
CAN injection, where thieves access wiring — frequently through a headlight unit or wing — and inject messages onto the vehicle's internal network telling it the key has been validated.
OBD port programming, coding a blank key via the diagnostic port.
Signal jamming of the locking command, so the car never locks when the owner walks away.
What actually helps:
A Faraday pouch or tin for the key, which blocks the signal entirely. Cheap and effective — but test it, because many pouches perform poorly or degrade.
Motion-sensing keys, which many manufacturers now fit, disabling transmission when the key has been still for a period. Check whether yours has this and whether it is enabled.
Turning off keyless entry where the car allows it.
A physical steering lock, which is visible, slow to defeat and consequently an effective deterrent.
An aftermarket immobiliser requiring a separate tag or code.
Keeping keys away from external walls, doors and windows, which matters more than people expect.
Tracking devices, which aid recovery rather than prevention.