What Is a Relay Attack to Steal a Keyless Car?

A relay attack is a method of keyless car theft where two criminals use electronic devices to capture your key fob's signal from inside your home and relay it to your car, tricking it into unlocking and starting as if the genuine key were right beside it.

It typically takes under a minute, requires no broken glass or forced entry, and now accounts for somewhere between 58% and 70% of all vehicle thefts in the UK depending on the data source.

Here's exactly how it works, why it's become so common, and what genuinely stops it.

How a Relay Attack Actually Works

The attack relies on a fundamental design quirk in keyless entry systems. Your car constantly emits a low-power signal asking whether an authorised key is nearby, and your key fob answers automatically the moment it's within a short range, unlocking the doors and enabling the ignition without you pressing anything.

Criminals exploit this passive exchange using two coordinated devices and, usually, two people:

• Device one is held near your front door, car, or wherever the key happens to be inside your home, capturing the weak signal your fob constantly broadcasts, sometimes from over 100 metres away
• Device two is held next to the target car, receiving the captured signal and rebroadcasting it directly to the vehicle
• The car "hears" what it believes is the genuine key responding from close range, so it unlocks the doors and allows the engine to start
• The thieves drive away, often within under a minute, without ever touching the actual key or triggering the factory alarm

Crucially, no alarms sound and no glass breaks during this process, since as far as the vehicle's electronics are concerned, the correct key was genuinely present and used normally.

Why Relay Attacks Have Become So Common

The scale of the problem has grown dramatically in recent years. Data from the Crime Survey for England and Wales shows 58% of car thefts between March 2023 and March 2024 involved criminals manipulating keyless entry signals, while the Association of British Insurers puts the figure for stolen vehicles taken via relay methods at 70% for 2024.

Some more recent analysis suggests the proportion has climbed even further, with one source citing 62% of all theft now attributable to keyless or relay attacks specifically.

Context helps explain the trajectory too. Relay attacks made up just 14% of UK car thefts back in 2019, meaning the method has grown roughly fourfold in under five years as the equipment required has become cheaper, smaller and easier to obtain. In London specifically, keyless theft is estimated to account for around 60% of all vehicle thefts recorded by the Metropolitan Police.

Which Vehicles Are Most at Risk

Relay attacks specifically target vehicles with keyless entry and keyless start systems, sometimes called passive entry, passive start. If your car allows you to unlock the doors and press a start button without physically inserting a key, it's technically vulnerable to this method, regardless of make or price point.

Higher-value and newer vehicles tend to be disproportionately targeted simply because they're more likely to have keyless technology fitted as standard, and because the resale or export value makes the effort worthwhile for organised theft groups. That said, the underlying vulnerability exists on any keyless model, not just premium marques.

The Limits of Faraday Pouches and Steering Locks

Signal-blocking Faraday pouches remain one of the most commonly recommended defences, and they genuinely work by preventing your key's signal from escaping the house in the first place. The catch is that they only work if you remember to use them every single time, and a worn or damaged pouch can quietly stop blocking signal without any obvious warning sign.

Visible deterrents like steering wheel locks add friction too, making a stolen car harder and slower to actually drive away with even if the relay attack itself succeeds. Both are worth having, but neither closes the underlying vulnerability at the vehicle level, since a determined thief who successfully relays your signal still gains full access and a working ignition.

Why a CAN Bus Immobiliser Stops Relay Attacks Completely

This is where a genuinely different layer of protection matters. A relay attack works specifically because the car trusts the signal it receives without any additional check. A CAN bus immobiliser removes that blind trust by requiring a second, entirely separate form of authorisation before the engine will actually run, one that has nothing to do with the key fob's signal at all.

GPSBob's Casper Ghost-Like Car Immobiliser works exactly this way, connecting directly into your vehicle's CAN bus network so it communicates seamlessly with your car's onboard electronics rather than sitting as a bolt-on box. Even if a relay attack successfully tricks your car into unlocking and the ignition into starting, the vehicle remains genuinely inoperable until a specific sequence of button presses, known only to you, is entered using controls already inside the car, on the steering wheel, dashboard or door panels.

Because there are no visible fobs, switches or indicators, there's nothing for a thief to spot, scan or bypass.

Casper Ghost-Like Car Immobiliser Features

• CAN-BUS technology that renders the vehicle inoperable without the correct sequence
• Completely invisible installation with no key fobs or physical indicators
• Compatible with a wide range of vehicles, including cars, vans and motorcycles
• Professional installation that preserves the vehicle's original wiring and architecture
• Priced at £399.00 as a one time payment, with installation included

Casper Pro: No Tag, No Start Features

For drivers who'd rather not remember a manual sequence, the Casper Pro takes an automated approach instead. Rather than entering a code, the system recognises an encrypted tag automatically the moment it's present in the vehicle, allowing the car to start as normal, while the engine simply won't run without it.

• Anti-scan technology and direct control over key engine functions
• Seamless integration with no impact on the vehicle's aesthetics or functionality
• Compact, discreet design that stays hidden from would-be thieves
• Suitable for a broad range of vehicles, including older models without factory keyless systems
• Priced at £499.00 as a one time payment, with installation included, and fitting typically takes around an hour

Pros and Cons of a CAN Bus Immobiliser Against Relay Attacks

Weighing up the genuine strengths against the practical trade-offs helps clarify why this approach outperforms passive deterrents alone.

Pros:

• Closes the specific vulnerability relay attacks exploit, rather than just making theft slower or more visible
• Works even if the key fob signal is successfully relayed or a key is physically stolen
• Completely invisible installation, leaving nothing for a thief to identify or bypass
• No ongoing subscription cost once professionally fitted

Cons:

• Requires professional installation, so it isn't something you can fit yourself
• Manual PIN entry (on the standard Casper) adds a small extra step to your usual routine
• Doesn't replace the need for basic habits like a Faraday pouch, since layered protection remains the strongest overall approach

Browse GPSBob's Range of Immobilisers

Ready to close the gap that relay attacks exploit? Take a look at GPSBob's range of Casper immobilisers to find the right fit for your vehicle.

FAQs

Can a relay attack work on a car parked inside a locked garage?

Generally no, since the metal structure of a garage typically blocks or significantly weakens the signal needed for a relay attack to succeed, making it a genuinely effective physical barrier.

Do all modern keyless cars have the same level of vulnerability to relay attacks?

No, some manufacturers have introduced motion-sensing key fobs that stop transmitting when stationary, which reduces but doesn't always eliminate the risk compared with older keyless systems.

Is it illegal to own the equipment used to carry out a relay attack?

Owning certain signal amplification devices isn't automatically illegal, but using them to gain unauthorised access to a vehicle is a criminal offence under UK law.

Can a relay attack be used to steal items from inside a car without taking the vehicle itself?

Yes, the same signal relay method can be used simply to unlock a car and steal contents from inside without driving it away, which is a less reported but genuinely common variant.

Does turning off a key fob's wireless signal completely prevent a relay attack?

Yes, if your specific key fob model supports manually disabling its wireless signal, doing so removes the relay attack risk entirely for as long as it stays switched off.