The relay attack has become the fastest-growing car theft method in Europe. It exploits a flaw in the keyless system to unlock and start a vehicle without forcing a single lock. Understanding the mechanism is the first step in protecting yourself effectively.
The relay attack is a no-break-in theft technique that targets vehicles fitted with keyless entry and start (smart key). Unlike a classic theft with broken glass or picked lock, this method leaves no visible trace on the vehicle.
The principle relies on amplifying the radio signal permanently emitted by the keyless key, even when it sits inside your home. Two accomplices equipped with electronic relays work together:
These amplification devices are unfortunately available online for a few hundred euros, which explains the surge in this type of theft.
In theory, every vehicle fitted with a keyless system or smart key is vulnerable to a relay attack. However, some brands and models are statistically more targeted, due to their resale value or the ease of exploiting their systems.
SUVs and premium vehicles are particularly targeted because of strong demand in the parallel parts market and for export.
If your vehicle has a "Start/Stop" button and you never need to take your key out of your pocket to unlock or start it, your car probably has a keyless system and is therefore potentially vulnerable.
To grasp the threat, here is the precise unfolding of a relay-attack theft, step by step:
Thieves spot a keyless vehicle parked outside a home. They usually operate between 2am and 5am, when owners are asleep and the key is often left in the hallway.
Device 1, positioned near the house (against the front door, under a window), captures the low-frequency radio signal emitted by the key. This signal, normally limited to 1-2 metres of range, is amplified and transmitted to the second device.
Device 2, held by the accomplice near the vehicle, receives the amplified signal and retransmits it to the car. The vehicle then detects what it interprets as the legitimate key nearby.
The vehicle unlocks its doors. The thief gets in, presses the Start button and the engine starts. The whole operation takes under 60 seconds in most cases.
Once the engine has started, the vehicle keeps running even if the signal is cut. The thief can drive without limits as long as they do not switch off the engine. That is why these vehicles are often driven straight to a storage or dismantling location.
Several affordable and low-cost solutions considerably reduce the risk of relay-attack theft.
The Faraday pouch (also called a signal-blocking pouch) is the simplest and most widely used solution. This small pouch lined with metal fabric completely blocks the radio signals emitted by your keyless key:
If you do not have a Faraday pouch, a simple airtight metal box (a metal biscuit tin will do) can block your key's signal. Drop your keys in each evening. Test signal blocking the same way as with a Faraday pouch.
Some vehicles let you temporarily disable the keyless function via the dashboard menu or a button combination on the key itself. Check your owner's manual or contact your dealership to find out the exact procedure for your model.
Faced with the scale of the issue, car manufacturers have developed technological counter-measures built straight into vehicles and next-generation keys.
BMW and Jaguar Land Rover were among the first to embed a motion sensor (accelerometer) in their keys. When the key is still for several minutes (placed on a piece of furniture, for example), it stops emitting its radio signal. This makes relay attacks ineffective during rest periods.
UWB (Ultra Wideband) technology represents the major step forward in keyless security. Unlike a classic radio signal, UWB allows precise measurement of the exact distance between the key and the vehicle:
Some manufacturers offer software updates (OTA or at the dealership) that strengthen the security of the communication protocol between key and vehicle. If your vehicle is eligible, contact your dealership to check it is up to date.
If you bought a used vehicle with keyless, ask the manufacturer about available security updates. Some critical patches were issued after the initial release of the vehicle.
If you find your vehicle gone with no trace of forced entry, a relay-attack theft is very likely. Here are the steps to take immediately:
Go to the police station as soon as possible. Make clear it is a no-break-in theft, probably by relay attack. Filing a report is essential for any insurance procedure.
Contact your insurer within 48 hours of discovering the theft. Send a copy of the police report and describe the circumstances (no trace of forced entry). Most comprehensive contracts cover this type of theft, but supporting documents may be requested.
To dig deeper into your cover, see our guide on car key replacement and pricing.
If your vehicle is recovered, it is essential to reprogram the immobiliser and all keys. Data captured by thieves could be reused for another attempt. A qualified auto locksmith can carry out this work.
Put in place the protection solutions described in this article: Faraday pouch, disabling keyless at night, and possibly an additional mechanical lock.
Reprogramming the immobiliser and keys after a relay-attack theft is a technical step that needs professional equipment and specific know-how.
The first operation consists of removing every key registered in the vehicle's ECU. This ensures the data captured by thieves (codes, digital fingerprints) become unusable. Complete clearing of the ECU key memory is essential.
New keys are then programmed and paired with the vehicle. This work involves:
To understand the different key technologies, see our article on types of car keys: transponder, remote fob and keyless.
At DKP, our technicians attend on site to carry out full immobiliser reprogramming after a relay-attack theft. The call-out covers:
For more on the technical process, see our guide on car key programming.
DKP intervient en urgence 24h/24 pour tout problème de clé véhicule, partout en France et Belgique.
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