By Emran Russell, Diploma in Engineering in Power Technology (Feni Polytechnic Institute), diagnostic training at TWEEN Automobile School. Reviewed: September 2026, next scheduled review in six months, since manufacturer countermeasures and reported prevalence change. This article explains the mechanism at the level an owner needs to defend against it and stops there: no equipment is named and no operational detail is given, even where source material offered it. Your vehicle and situation may differ, so check with your manufacturer or dealer about what your own model already includes.
Relay theft is when two people extend the short-range conversation your keyless fob and car normally have only while the fob is close by, one device positioned near the fob, often just inside a front door, and a second near the car, so the car reads the relayed signal as the key being present and unlocks or starts. No physical key theft and no forced entry occurs. Protection is layered, not a single fix, and newer models increasingly ship with countermeasures already built in.
What relay theft actually is: the convenience feature turned against itself
Passive keyless entry exists so you never have to take the fob out of your pocket: the car and the fob continuously exchange a short, low-power conversation, and when the car confirms the fob is genuinely close by, it unlocks itself and allows the start button to work. That convenience is the entire vulnerability. Relay theft does not break the car's security system or crack a code; it extends a conversation the car was only ever designed to have at close range across a distance it was never meant to cross, using two coordinated devices that pass the signal between them. The car has no way to tell that the "nearby" fob is actually being relayed from somewhere else, because the conversation itself looks completely normal.
What relay theft is not
Owners tend to lump every keyless-adjacent theft into "relay theft," and the distinction matters because the protections are different. Key cloning duplicates a physical key's code or chip, usually requiring the thief to get close enough to a working key with cloning equipment, a separate vulnerability from a relayed signal. Reprogramming a blank key through a vehicle's diagnostic port requires the thief to already be inside the car, and it bypasses the fob conversation entirely rather than exploiting it; our piece on OBD port locks and aftermarket immobilizers covers that separate attack path and what addresses it. And plain theft of a spare key left somewhere visible or unsecured is not a technology attack at all, it is a physical security lapse. None of these are relay theft, and a defense built for one does not necessarily cover the others.
Why some cars are more exposed than others
Exposure to relay-style attacks is not uniform across vehicles, and it has changed over time as manufacturers responded. ADAC, the German motoring club, ran a widely reported round of relay-attack testing across 237 keyless models; its findings, published and analyzed alongside the UK consumer group Which? in January 2019, found 230 of the 237 vehicles tested could be unlocked and, in most cases, started using a relay-style method, while only three models, all from Jaguar Land Rover at the time, resisted it. In the United States, the National Insurance Crime Bureau documented in a 2016 investigation that a relay-style device it obtained was able to unlock more than half of the vehicles it tested and start and drive off in most of those. Since then, manufacturers have added countermeasures at different times, including motion-activated fob sleep modes and distance-checking technology in some newer models, which is why a newer car may already be meaningfully better protected than an older one, and why checking your own model with your manufacturer or dealer is worth doing rather than assuming either way.
Keep the fob away from the front of the house, windows and doors
Because passive entry only requires proximity, where the fob normally sits at home matters. A fob left on a hook by the front door, on a kitchen counter near a window, or anywhere close to an exterior wall sits exactly where a relay-style attack is aimed. Moving the fob further into the house, away from exterior doors and windows, reduces the opportunity available to this specific method. This is not a guarantee against theft, and it will not help at all against a smashed window or a car loaded onto a tow truck, but it is a free, permanent change to a habit that costs nothing and directly addresses the distance this attack depends on.
Check whether your fob has a motion-activated sleep mode
Many newer keyless fobs are designed to stop broadcasting after a period without movement, a motion-activated sleep mode, and most owners have simply never checked whether theirs has it or how it behaves. This detail varies by manufacturer and model: some fobs enter sleep mode automatically after a set period of stillness, others require an action from the owner, and some older fobs do not have this feature at all. Rather than guess, check your owner's manual or ask your dealer whether your specific fob supports it and what triggers it. If your fob does have this feature, understanding it is free security you already own and may not be using.
Use a blocking pouch or box, and test it
A pouch or box that fully blocks the fob's signal stops it from being detected at all while it's sealed inside, which addresses the relay-attack vulnerability directly by removing the fob from the conversation entirely. The word "fully" matters: not every pouch or box sold actually blocks the signal completely, and the only way to know is to test the one you own rather than trust the packaging. Our guide to testing whether your faraday pouch actually works walks through that test step by step, and our comparison of a signal-blocking box, pouch, or relying on your fob's own sleep mode covers which form factor fits which situation.
Add a layer that does not depend on the radio at all
Every defense above is still ultimately about managing a radio signal, and a determined thief working around one radio-based defense does not have to solve a second, unrelated problem if that is the only layer in place. A device that does not depend on the fob's signal at all, a visible mechanical lock on the steering wheel, or an immobilizer added at the OBD port, adds a barrier a relay-style attack has no way to address on its own, because it never touches the fob conversation in the first place. Our breakdowns of whether steering wheel locks are worth it and OBD port locks and aftermarket immobilizers cover what each actually adds. None of this amounts to a guarantee; it is about making a car a meaningfully harder, slower target, which is the honest limit of what any of these layers can promise. Our cluster guide to anti-theft gadgets that actually deter a thief walks through how the layers fit together as a whole approach.
| Layer | What it addresses | What it does not address |
|---|---|---|
| Fob placement (away from doors/windows) | Reduces opportunity for a relay-style attack | Does nothing once a thief is inside or has a spare key |
| Motion-activated sleep mode | Limits the window the fob is broadcasting | Depends entirely on your specific fob supporting it |
| Tested blocking pouch or box | Removes the fob from the radio conversation entirely | Only as good as the seal; an untested one may not work at all |
| Steering wheel lock or OBD port lock | Adds a physical, non-radio barrier | Does not stop a relay attack itself, but slows or deters the thief after one |
FAQ
How does relay theft actually work on a keyless car?
Two people work together with two devices: one picks up the signal from your fob, often through a wall or door, and relays it to a second device held near the car. The car reads that relayed signal as the key being genuinely nearby and unlocks or starts, without you ever taking the fob out or the thief touching it.
Is relay theft the same as hacking my car?
No. It does not break into the car's computer or crack any code. It exploits the fact that the car and fob are designed to trust a nearby signal, by extending that signal further than it was meant to travel.
Does a Faraday pouch stop relay theft completely?
A pouch that genuinely blocks the fob's signal removes it from the conversation entirely, but not every pouch sold actually seals completely. Testing the specific pouch you own, covered in our pouch test guide, is the only way to know it is doing its job.
Are newer cars safe from relay theft?
Some are meaningfully better protected than older models, since manufacturers have added countermeasures like motion-activated sleep modes and distance-checking technology at different times. Whether your specific model is protected, and how, varies, so check with your manufacturer or dealer rather than assume.
Can relay theft happen if my key is in a drawer across the house?
It becomes harder the further the fob is from the exterior of the house, since the attack depends on capturing a usable signal in the first place. Moving the fob away from doors and windows reduces the opportunity, though it is not a guaranteed fix on its own.
Is relay theft the same as someone cloning my key or stealing my spare?
No, and this is a common mix-up. Key cloning duplicates the physical key's code, and losing or leaving out a spare key is a physical security lapse, not a signal-relay attack. Each requires a different kind of protection.
What's the single best defense against relay theft?
There isn't one single best defense; owners who take this seriously typically layer several: keeping the fob away from exterior doors and windows, checking for and using a sleep mode if the fob supports it, testing a blocking pouch or box rather than trusting it, and adding a radio-independent layer like a steering wheel lock. No layer here is a guarantee, and your own vehicle's protections are worth confirming with your manufacturer or dealer.