Keyless Relay Theft and Faraday Pouches

A relay attack does not fool the car. It tells the car the truth about a key that is further away than it should be. Two devices bridge the gap: one near the car, one near the house. The car asks for the key, the key answers, and the answer is simply carried further than the manufacturer intended.

That is why the fix is at the key rather than the vehicle. If the key cannot hear the request, there is nothing to relay — which is how a cheap fabric pouch addresses the attack more directly than anything fitted to the car.

A note on this guide: this rests on how the attack and the countermeasures work, not on equipment tested against an attack here. See how we test.

The problem, as it appears

A car that was locked, undamaged, and gone. No broken glass, no forced lock, and frequently no alarm.

Because from the car's point of view nothing improper happened. The correct key was present and responded correctly. The entire event looks, in the car's own logs, like a normal unlock and start.

Why the alarm and the immobiliser disappoint

Because both are working exactly as designed.

An immobiliser prevents the engine running without an authorised key. A relay attack presents an authorised key. There is nothing for the immobiliser to object to — the check passes because the key genuinely answered.

The same is true of the alarm. It is looking for forced entry, and there was none.

This is worth understanding because it explains why the manufacturer's security is not the failure. The weakness is a design decision that traded a small amount of security for the convenience of not taking the key out of your pocket, and it lives in the key rather than in the car.

What actually matters

The pouch is the direct answer, and it fails silently

A working faraday pouch stops the attack completely. The physics is not marginal — either the signal gets out or it does not.

The problem is that the failure mode is not gradual. The conductive lining cracks with folding, use and time, and a pouch that worked when it was bought can be doing nothing a year later while looking identical.

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Test it, and keep testing it

The step that separates a pouch from a decoration, and it takes thirty seconds.

Put the key in, close it properly, and walk up to the car holding the pouch. Try the door handle and the start button. If either responds, the pouch is not blocking.

Do this when it arrives — some are poor from new — and every few months afterwards. This is the only part of this page that requires ongoing attention, and it is the part most likely to be skipped.

The spare key matters as much as the daily one

The gap people leave open.

A carefully pouched daily key and a spare sitting in a kitchen drawer near the front of the house is a solved problem next to an unsolved one. Both keys need the same treatment, and the spare is the one that never gets thought about because it is never used.

Check whether your key already sleeps

Free, and it may change how much you need to do.

Many newer keys have a motion sensor and stop transmitting after a period without movement. A key like that, left on a hall table overnight, is not answering anything.

If yours does this, the pouch still matters — for the key in a coat pocket by the door, or in a bag that gets moved — but the overnight case may already be covered. It is worth finding out rather than assuming either way.

Where the key sits in the house is free to change

Costs nothing and reduces the range the attackers have to work with.

Away from the front door, away from windows, and not on a metal surface that can act as an accidental antenna. This does not solve the problem on its own, and it makes the attack harder for no money.

A physical lock addresses a different question

Not an alternative to the pouch — a different layer, answering a different question.

The pouch defeats one specific attack. A visible steering lock addresses selection: whether a thief chooses your car over the one parked next to it, and whether they persist once they are in.

It also covers methods that have nothing to do with the key at all, which is why the two together are the sensible arrangement rather than a redundancy.

The honest assessment of what these do and do not achieve, including why they are more relevant on a keyless car than on the cars they were designed for, is in are steering wheel locks still worth using.

The OBD port is the other well-known route

Worth knowing about, and worth keeping in proportion.

The diagnostic port can be used to program a new key on some vehicles, which is a route that does not involve your key at all. Port locks exist and are cheap.

Two caveats stated honestly: they are an obstacle rather than a barrier, and anything fitted to a diagnostic port needs to come off easily for legitimate servicing. Treat it as one more thing that takes time rather than as a solution.

Evidence, if it happens anyway

A camera with parking mode records the approach, which is the part CCTV usually misses and the part that establishes what happened.

That is a genuine benefit and it comes with a genuine cost, because parking mode is the feature that drains batteries — a dashcam that does not flatten the battery covers doing it without waking up to a flat car.

What this page will not tell you

Whether your specific model is vulnerable. That changes with firmware, model year and market, and manufacturers have made real improvements. A page stating it would be wrong within a year and believed anyway.

Anything about how to perform the attack. The mechanism is described here only to the extent needed to explain why the countermeasure is at the key.

Check current advice from your manufacturer and from your insurer — the second one matters, because some policies now ask specifically about how keys are stored.

The order to work in

1. Find every key, including the spare nobody uses.
2. Get a pouch for each, and test each one against the car.
3. Re-test every few months. They fail silently.
4. Move where keys live — away from the door, away from windows.
5. Check whether your key sleeps when stationary.
6. Add a visible physical lock for the selection problem.
7. Consider a port lock as an obstacle, not a solution.
8. Check what your insurer asks about key storage.

The mistake to avoid

Buying a pouch and never testing it. It is a cheap piece of fabric that lives folded in a pocket, its conductive lining cracks with use, and it gives no indication when it has stopped working — so the most likely version of this failure is somebody with a pouch, using it faithfully, protected by nothing. The test takes thirty seconds and it is the entire difference.

The second mistake is protecting one key. The daily key gets the attention because it is the one in your hand; the spare sits in a drawer near the front of the house for years, transmitting, and it is just as good to a relay attack as the one you were careful with.