Your car key is not shouting from the hall table, it is answering a question thieves asked for it
Nothing is forced, nothing is broken, and the car pulls off the drive as though you had unlocked it yourself.
Keyless entry is the feature nobody asks for and nobody gives back. You walk up with the key in a coat pocket, the handle unlocks, you press a button and you drive. It is genuinely pleasant, and what it replaced was a mechanical act, a cut piece of metal turning in a lock, with a radio conversation that happens automatically and invisibly several times a second whenever you come near the car. That conversation is the vulnerability, and the way it is usually described is wrong in a way that matters. Your key is not sitting on the hall table shouting its identity into the night. It is asleep, and it is waiting to be asked something. Relay theft works because two people with two cheap boxes can carry the car's question to your key and carry the key's answer back, across a garden wall, through a front door, up a flight of stairs. The car receives a correct answer from a key it believes is standing at the handle, so it does exactly what it was built to do. No forced lock, no broken glass, no alarm, and in the morning no evidence that anything happened at all except an empty space.
It is a relay, not a hack
The door handle of a keyless car emits a very weak low-frequency signal, deliberately weak, good for a metre or two at most. That signal is the car asking whether its key is present. The key wakes up, answers on a different and higher frequency with a rolling code the car can verify, and the doors release. Nothing in that exchange is broken by the thieves. One of them stands at your front door or under a window with a device that picks up the car's question and retransmits it at strength; the other stands at the car with the matching half. Your key, wherever it lies in the house, hears a question it has no way of knowing arrived by an unusual route, and it answers honestly. The code is never copied, never stored and never cracked. It is simply carried further than the engineers intended. That is why the attack takes seconds rather than minutes, needs no knowledge of your particular car, and leaves your key perfectly valid afterwards. It is also why it fails completely the moment a car can work out how far away its key genuinely is.
One technology stops it, and it is not one you can add later
ADAC has been running this test since 2016 and has now put more than 850 models past the same relay equipment. Around 70 percent of the cars tested are better protected than they used to be, and roughly three in ten still unlock and drive away. Across that decade only one thing has resisted the equipment outright: ultra-wideband, usually written UWB. Rather than ask whether the key can hear it, a UWB car measures how long a radio pulse takes to reach the key and come back. Radio travels at a fixed speed, so time is distance. A relay box can add delay to that journey but it cannot subtract any, so the car sees a key claiming to stand at the door handle while reporting a flight time of forty metres, and it refuses. Jaguar Land Rover has fitted it since 2018 and the Volkswagen group since 2019 across Audi, Cupra, Seat, Skoda and Volkswagen, with BMW, Mercedes, Hyundai, Kia, Genesis and Suzuki on a growing list of individual models. It is not an option you can retrofit. Either the car was built with it or it was not, and ADAC publishes the list of which is which.
The motion sensor in your key helps less than it sounds
Plenty of fobs built since roughly 2019 contain a small accelerometer and stop answering after a spell of complete stillness, typically somewhere between forty seconds and a few minutes depending on the manufacturer. ADAC found the feature in 115 of the cars it tested and still rates that protection as clearly weaker than ultra-wideband, for a reason that becomes obvious the moment you picture an ordinary evening. The key is only asleep while it is genuinely undisturbed. A key in a coat pocket in a restaurant is awake. A key on a shelf against a wall that a bus rumbles past is awake. A key you moved twenty seconds ago on your way up to bed is awake, and someone standing at your door is patient enough to wait it out or lucky enough to arrive first. A sleeping key is a good thing to have. It is not a plan.
The pouch works, and most people use theirs wrong
A Faraday pouch, a signal-blocking wallet or a plain metal tin with a lid puts a conductive shell around the key, and a properly closed shell stops a radio conversation dead. It costs less than a tank of fuel, needs no wiring, works on any car regardless of age, and it is the only real countermeasure available to somebody whose car was built without ultra-wideband. The mistakes are remarkably consistent. People buy one pouch and leave the spare key in a kitchen drawer, which is the key the thieves will reach anyway. They fold the flap over instead of pressing the seal shut along its whole length. They use it faithfully for a month and then stop. And almost nobody tests it. Testing takes thirty seconds: seal the key in, walk to the car, pull the handle, then sit inside with the sealed pouch on your lap and press the start button. If anything at all responds, the pouch is not doing its job. Repeat that check every few months, because linings wear out with handling long before the pouch looks tired.
Relay theft is not the only way a modern car leaves without you
Two other methods have grown up alongside it and neither involves your key at all. In the first, a thief reaches the wiring loom behind a headlight or a wing mirror and injects messages onto the car's own internal network telling it that a valid key is present. In the second, a device is plugged into the diagnostic socket inside the cabin and a fresh key is programmed in minutes. Ultra-wideband does nothing against either, and neither does a pouch, because your key was never part of the conversation. What both need is physical access and uninterrupted time, which is why the unfashionable answers still earn their place: a visible steering lock, a gate, parking nose in against a wall so the front of the car is unreachable, an aftermarket immobiliser or a tracker. None of them makes a car impossible to steal. All of them make it a worse choice than the car parked next to it, which is the only outcome any of this can honestly promise. And if the car is never recovered, remember that the payout your insurer offers is an opinion you are allowed to argue with.
What to actually do
None of this is an argument for giving up keyless entry. It is an argument for finding out which of two situations you are in, because the correct response is completely different depending on how your car was built.
Find out first whether your car uses ultra-wideband. ADAC publishes a free and regularly updated list of every model it has tested. If yours is on the protected side, relay theft is not your problem and you can stop buying pouches.
If it is not, check whether the keyless function can be switched off. Many cars allow it somewhere in the infotainment menu, and on a good number of others a double press of the lock button on the fob puts the key to sleep until you press a button again. Your handbook names the feature.
Buy a pouch for every key. The spare in the drawer, the one at your parents' house and the one you have not touched since delivery all open the same car.
Test the pouch rather than trusting it. Sealed key, hand on the door handle, then the start button from inside. Repeat every few months.
Move the keys away from the front of the house. Two extra walls and five metres cost nothing and sit right at the edge of what a relay can comfortably bridge.
Add something physical and visible. A steering lock will not defeat a determined thief, but it moves you down the list before anybody starts.
Know where every key you were given actually is. Insurers routinely ask for all keys to be produced after a theft claim, and a key you cannot account for is the fastest route to a difficult conversation.
When you sell, hand over every key and state how many there are in the advert. Buyers of privately sold cars are right to count them, and a key you kept is a key that still starts a car you no longer own.
Frequently asked questions
Does wrapping the key in aluminium foil work?
Sometimes, and unreliably. Foil is conductive so it does weaken the signal, but a wrapped key has folds, gaps and thin spots, and the wrap is slightly different every night. It is a demonstration rather than a defence. A biscuit tin with a steel lid, a metal box or a purpose-made pouch all give a consistent result, and all three should be tested the same way. Never use the microwave. It is not designed as a shield, it does not reliably behave as one with the door closed, and a key that is inside when somebody switches it on is destroyed.
If thieves relay my key, is the key compromised afterwards?
No, and this is one of the few reassuring facts here. A relay attack copies nothing at all. It carries one live conversation and then it is over, so the rolling code in your key is untouched and the key is exactly as secure as it was the day before. Losing a car this way does not mean the remaining keys are unsafe, although if the car is recovered many owners have the locks recoded anyway and some insurers will insist on it.
My car has ultra-wideband. Am I finished?
Against relay theft, essentially yes, and that is exactly why it is worth checking rather than assuming. Against everything else, no. Ultra-wideband solves the distance problem and nothing more, so a car with a diagnostic socket in the cabin and a wiring loom behind a headlight is still worth protecting physically. It also does nothing at all if somebody simply takes the key off you, which remains the oldest method there is.
Is an older car without keyless entry safer?
From this particular attack, yes. A car whose key has to be physically in a lock or a slot has no conversation to relay, and that is a genuine security advantage of a slightly older car. Its weakness lies elsewhere, usually in an immobiliser generation that a diagnostic tool defeats more easily, so the physical deterrents matter just as much.
Will my insurance pay when there is no damage at all?
Usually, and the absence of damage is what makes the claim awkward rather than impossible. Policies across Europe are written around theft, not around forced entry, but with no visible break-in the burden falls on you to show the car was locked and the keys were kept sensibly, which is why every key gets asked for. Report it to the police immediately and get the report number, tell the insurer the same day, and say plainly that you believe it was a relay theft. It is a recognised and widely documented method, not an exotic excuse, and naming it early tends to save a fortnight of correspondence.
