A private investigator has revealed a simple and inexpensive method to protect cars from keyless theft: placing car keys inside a metal biscuit tin. The technique acts as a Faraday cage, blocking the signal that thieves boost to unlock and start vehicles.
Thousands of Cars Stolen Annually
In 2025, thousands of cars were reported stolen in the UK, with roughly ten vehicles swiped from driveways and car parks every 10 minutes. Christopher Thomas, an investigator with UK Private Investigators, has worked on numerous stolen-car recovery cases and warns that many car owners make a critical mistake that turns their cars into easy targets for theft in less than 10 seconds.
Thieves Exploit Keyless Entry Signals
Keyless car theft devices are sold on the dark web for upwards of £15,000, but criminals with basic knowledge can build their own relay-boosting devices for just a few hundred pounds. According to Thomas, the biggest mistake car owners make is leaving their keys too close to the door. He said: "Your car sends out a signal every few seconds looking for your key. When your key is in range, it talks back to your car and opens it."
Leaving keys by the front door makes it easy for thieves to pick up the signal and steal the car. While signal-blocking pouches are available online, not all are effective, and Thomas advises testing them before relying on them.
The Biscuit Tin Solution
A cheaper and effective alternative is a metal biscuit tin. Thomas explained: "We have all seen these biscuit tins in the shops or in people's homes. While it's a bit strange, putting your keys in one of these tins stops your car key from broadcasting the signal back to the car, even when boosted."
He recommends a simple test: "All you need to do is get someone in your household to phone your mobile phone, then put your phone in the tin. If the line goes dead, then the tin will work for your car keys too."
Metal tins work like a Faraday cage, blocking or weakening the signal from the key, leaving little to no signal for thieves to boost. Without that signal, the car becomes much harder to steal.
