How to Prevent Keyless Car Theft (Relay Attacks)
To prevent a relay attack on a keyless car, block or disable your key fob''s signal when it is not in use: store the key in a Faraday pouch or metal box, keep it away from external doors and windows, and switch off the fob''s wireless function if your model supports it. Relay attacks work by capturing and amplifying the signal your key broadcasts from inside your home, so the car believes the key is beside it — which means the defence is simply to stop that signal escaping.
The attack takes under a minute, requires no damage to the vehicle, and leaves no broken glass. Understanding it is what makes the countermeasures obvious.
How a relay attack works
Keyless-entry cars are constantly listening for their key. When the fob is close enough, the car unlocks and allows the engine to start. The fob does not need to be pressed — proximity is the whole authentication.
A relay attack exploits exactly that. Two people work together with a pair of radio relay devices. One stands near your house, close to wherever the key is kept — beside a front door, a hallway table, a window. Their device picks up the faint signal your fob is emitting and amplifies it. The second person stands beside your car with the paired device, which rebroadcasts that amplified signal. The car receives what looks like your key at close range, unlocks, and permits ignition. The pair drive away.
Nothing is forced, nothing is hacked in the conventional sense, and the car''s own security worked exactly as designed. The signal was simply stretched across the distance between your hallway and your driveway.
The signs a relay attack may be a risk
There are rarely dramatic signs — the whole appeal of the method is its quietness. What raises the risk is circumstantial: a keyless-entry vehicle, keys kept near the front of the house, a car parked on a driveway or street within radio reach of where the keys sit, and a desirable model. Two people loitering near a driveway with what look like bags or small boxes is the only visible tell, and by the time it is noticed the car is usually gone.
How to stop a relay attack
The countermeasures are unglamorous and effective, because they all attack the same weak point: the signal leaving the key.
Use a Faraday pouch or box. A signal-blocking pouch lined with conductive material stops the fob''s radio signal escaping, so there is nothing to relay. This is the simplest and cheapest defence, and it works whenever the key is inside it. Buy one that actually blocks — test it by putting the key inside, closing it fully, and walking up to your car; if the car does not respond, it is doing its job. Retest occasionally, since linings wear.
Keep keys away from doors and windows. Distance weakens the signal and makes the amplification harder. A hallway table beside the front door is the worst possible place; an interior room is meaningfully better. This costs nothing.
Turn off the fob''s wireless function if you can. Many modern fobs have a sleep mode — often a button sequence, sometimes a motion sensor that disables transmission when the key sits still. Check your handbook; if the feature exists, use it.
Add a layer the signal cannot defeat. A visible steering-wheel lock, an OBD port lock, or a well-hidden tracker do not prevent the relay itself but make the car much harder to keep. Thieves choose easy targets, and visible physical deterrence moves you down the list.
Do not leave the spare key in the car, and store the spare with the same care as the main key. A spare in a kitchen drawer near the back door is a relay target too.
Faraday pouches: what to look for
A Faraday pouch works by enclosing the key in a conductive layer that absorbs and disperses radio waves. The details that matter are unfashionable ones: full closure (a gap or a partly folded flap defeats it entirely), a lining that has not cracked or worn thin with use, and a size that lets you seal it properly rather than forcing it shut. Test yours the day you buy it and again every few months, using the walk-to-the-car check above.
Keep the pouch where you would have kept the keys — the point is that it becomes the habit, not an occasional precaution.
One caution worth stating: a sleeve sold to block contactless payment cards is not the same product. Card sleeves are built for the 13.56 MHz frequency that bank cards and passports use, while a car fob transmits on a different, much lower band — and a card-sized sleeve will not physically hold a fob in any case. Buy a pouch specifically made for keys, and test it.
What if the car is already gone?
Report it to the police immediately with the registration and any tracker information, then to your insurer. Check whether your vehicle has a manufacturer-linked tracking service that can be activated. If you have a dashcam or doorbell camera, preserve the footage rather than overwriting it — relay thefts often capture the pair on camera, and the recording is useful evidence.
Relay theft, tracking, and the wider picture
A relay attack is about taking the car. A different concern — someone tracking where the car goes — involves a device physically attached to it, and is worth checking for separately if you have reason to think you are being followed. We cover that in how to find a GPS tracker on your car. Both come down to the same underlying idea: your vehicle is constantly emitting and receiving signals, and knowing which ones can be exploited is what lets you shut the gap.
For a printable reference covering vehicle checks, see our field guides, and for the detection equipment that finds a tracker once you suspect one, see our counter-surveillance range.
Keyless convenience was never meant to cost you the car. A pouch and a habit close the hole.
Frequently asked questions
What is a relay attack on a car? Two thieves use paired radio devices to capture the signal your keyless fob emits inside your home, amplify it, and rebroadcast it beside your car. The car believes the key is nearby, unlocks, and allows the engine to start — with no forced entry and in under a minute.
Does a Faraday pouch stop keyless car theft? Yes, when used properly. A Faraday pouch blocks the key fob''s radio signal so there is nothing for thieves to relay. It must be fully closed, and the lining must be intact — test it by sealing the key inside and checking that the car no longer responds when you approach.
Where should I keep my car keys to prevent theft? Away from external doors and windows, ideally in an interior room, and inside a Faraday pouch or metal box. Distance weakens the signal and the pouch blocks it entirely. Store spare keys with the same care.
Can you turn off a keyless car fob? Many modern fobs can be put into a sleep mode, either through a button sequence or an internal motion sensor that stops transmission when the key is left still. Check your vehicle handbook — if the feature exists, enabling it removes the signal a relay attack depends on.