What Is a Relay Attack and How Can You Protect Your Keyless Car?

What exactly is a relay attack?

A relay attack is a theft method in which the radio signal from a keyless car key is picked up and passed on to the vehicle, so the car behaves exactly as if the key were standing beside it.

To understand why this works, it helps to know how keyless entry operates. A proximity fob — the small remote you keep in a pocket or bag — constantly emits a faint, low-power radio signal. The car listens for that signal. When it detects the fob within a short range, usually a metre or two, it unlocks the doors when you touch the handle, and it allows the engine to start when you press the start button. The immobiliser, the electronic system that checks the key's identity before the engine control unit permits starting, is satisfied because the car believes the genuine key is present.

In a relay attack, thieves use electronic equipment to bridge the distance between the key and the car. The genuine fob might be on a hallway table while the car sits on the driveway; the relay equipment carries the fob's signal from one to the other. The car cannot tell the difference between the real nearby key and the relayed signal, so it unlocks and starts normally.

What makes relay attacks unsettling is how clean they are. There is no smashed window, no forced lock, no triggered alarm. The car simply appears to have been driven away by someone with a key — because, as far as the car's electronics are concerned, someone was.

Which cars are vulnerable to relay theft?

Any car with keyless entry and push-button start can be targeted by a relay attack, regardless of brand, price or age of the model.

This surprises many owners, because relay theft is often discussed alongside expensive vehicles. In reality, keyless entry is now common across mainstream cars — family hatchbacks, crossovers and estates as well as premium models. If your car unlocks when you pull the door handle with the fob still in your pocket, and starts with a button rather than a turned key, it uses the system that relay attacks exploit.

Cars without keyless entry are not vulnerable to this particular method. A vehicle that needs a physical key blade turned in the ignition, or a fob button deliberately pressed to unlock, does not constantly broadcast the signal that a relay attack needs. Those cars face different risks instead — which is why understanding your own key type matters. If you are unsure what kind of key you have, the differences are explained in plain terms in the guide to the various key designs on the road today.

One more point worth knowing: having two keyless fobs does not double the risk in the way people fear, but it does mean two signals exist to protect. The spare fob in a kitchen drawer is just as relayable as the one by the front door, so whatever defence you choose should cover every fob for the car, not just the one you carry.

How does a relay attack unfold?

In a typical relay attack, one person waits near the car while another gets close enough to the key — usually just outside the victim's home — and the key's signal is carried between them until the car responds.

The usual setting is overnight. The car is parked on a driveway or in front of the house; the key rests on a hallway table, a kitchen counter or a bowl by the front door — exactly where most of us leave it. The fob's faint signal reaches a short distance through walls and doors, which is all the thieves need.

Once the relayed signal reaches the car, events move at normal speed: the doors unlock at a touch of the handle, the start button brings the engine to life, and the car is driven away. Because the car believes the key is present, there is no alarm and no immobiliser intervention. The whole episode can be over very quickly, which is why relay theft is so rarely interrupted in progress.

It is worth being clear about what this explanation is for. Understanding the shape of the threat helps you choose defences — signal blocking, disabling keyless entry, physical barriers. It does not require, and this guide does not provide, any detail about the equipment involved or how it is operated. Those are matters for the police and the motor industry, not for car owners.

Can you tell if a relay attack has been attempted?

Usually you cannot tell at the time — a successful relay attack leaves no damage — but there are clues afterwards that are worth taking seriously.

The starkest clue is also the most obvious: the car is gone from the driveway with no broken glass, no damaged lock and no sign of forced entry. That pattern — a missing car and an undisturbed scene — is characteristic of keyless theft rather than a break-in. A car found unlocked in the morning when you are certain you locked it the night before is another warning worth investigating rather than dismissing.

Doorbell cameras and CCTV sometimes capture the aftermath: figures near the car in the early hours, or the car's lights flashing as it unlocks itself without you anywhere near it. If you have footage like that, save it — it is useful to the police.

A failed or interrupted attempt may leave no trace at all, which is genuinely frustrating. The practical response is the same either way: treat any unexplained unlocking as a prompt to tighten your defences and, if keys may have been compromised, to have the car reprogrammed. There is more on recognising interference with locks and handles in the guide to the signs that a car lock has been tampered with.

Faraday pouches and signal-blocking boxes

A Faraday pouch or box blocks the radio signal from your key fob, so there is simply nothing for thieves to relay.

The principle is straightforward. These products are lined with conductive material that absorbs the fob's radio emissions, creating a small shielded space. With the key sealed inside, its signal cannot reach the car — and a relay attack cannot begin. It is the closest thing to switching the key off without actually doing so.

Used properly, this is the simplest everyday defence available. The habit to build is: keys go in the pouch or box the moment you come home, and every fob for the car gets the same treatment, including the spare. A pouch used for one key while the spare sits unprotected on the sideboard leaves the job half done.

Test whatever you buy. With the key sealed inside the pouch, walk out to the car and try the door handle — the car should not respond. Repeat the test every few months, because pouches wear: linings crack, seams loosen and cheap products degrade faster than people expect. A pouch that worked in January is not guaranteed in December.

There are limits to be honest about. A pouch only protects the key while the key is inside it — it does nothing while you are out carrying the fob, and it is useless left open on the counter. For a deeper look at how well these products perform and where they fall short, the dedicated guide asks directly whether Faraday pouches really work for car keys.

Turning keyless entry off

Many cars let you disable keyless entry in the settings or with a button combination on the fob, which removes the relay risk entirely.

This is the most decisive defence of all, because it eliminates the vulnerability rather than shielding it. With keyless entry switched off, the car goes back to behaving like a conventional remote-locking vehicle: you press the fob button to unlock, and the constant proximity signal stops. No signal, nothing to relay.

How you do this varies by manufacturer. Some cars offer a keyless on/off option buried in the vehicle settings menu; some fobs can be put into a sleep mode with a particular button sequence; and some newer fobs contain motion sensors that stop transmitting when the key has been still for a while — a feature worth checking whether your car already has. Your handbook is the authoritative source, and a main dealer can usually disable the system if you cannot do it yourself.

The trade-off is convenience, and it is worth weighing honestly. Keyless entry is genuinely pleasant to live with, especially with arms full of shopping on a rainy evening in a Bromsgrove car park. Some drivers disable it permanently and never look back; others disable it only overnight via the fob's sleep function. Either approach is far better than leaving the system active with no other defence.

Layering defences that thieves avoid

No single defence is perfect, so combining several makes your car a poor target compared with easier ones nearby — and thieves, like water, take the easiest path.

Signal blocking and disabling keyless entry deal with the relay threat directly. Physical barriers deal with everything else, and they add a visible message that this particular car will be trouble. A steering wheel lock, for example, does nothing against a relayed signal — but it does mean the car cannot simply be driven away, relay or no relay. Thieves who spot one through the window often move on to a car without one.

The same logic applies to the car's diagnostic port. Some thefts work by accessing the OBD port — the socket mechanics use for diagnostics — to program a new key. A simple OBD port lock blocks that route. Driveway posts and bollards physically prevent the car from leaving; a tracking device does not prevent theft but greatly improves the odds of recovery. Good lighting, a doorbell camera and parking where the car is overlooked all add friction that opportunists dislike.

The table below compares the main options at a glance. Two of these have dedicated guides with more detail: the comparison of steering wheel locks against modern immobilisers, and the explanation of how an OBD port lock improves vehicle security.

What to do after a theft or a close call

If the car is gone, call the police first and then your insurer; if an attempt failed or keys may have been compromised, have the car's keys reprogrammed so the old key data no longer works.

For a completed theft, the order matters. Report it to the police straight away and keep the crime reference number — your insurer will ask for it. Then contact your insurer with the facts: where and when the car was taken, and anything you noticed, such as the car unlocking itself unexpectedly in previous nights. If you have doorbell or CCTV footage, preserve it.

For a scare rather than a loss — the car found unlocked, lights flashing in the night, a neighbour reporting strangers near the driveway — reprogramming is the sensible reset. When a car's keys are reprogrammed, the old key identities are deleted from the vehicle's memory and fresh ones are registered. Any key data the thieves may have captured becomes useless, because the car no longer recognises it.

A mobile auto locksmith can carry out reprogramming at your home or wherever the car is parked, and will verify your ownership before starting — as any trustworthy professional should. If the incident involved any damage to locks or handles, there is also practical guidance on what to do after an attempted car break-in.

Need help right now?

If your keyless car has been targeted, or you want the keys reprogrammed for peace of mind, a mobile visit is the straightforward route. The car key programming service covers reprogramming and replacement at your location, with ownership verified and a clear quote before any work begins. Call or WhatsApp 07367 634032 — the line is open 24 hours.