Drivers warned that signal-blocking key pouches ‘may not always work’

Motorists are being warned that signal-blocking pouches and boxes designed to thwart hi-tech car thieves may not work as advertised.

The devices, sometimes called Faraday pouches, have become popular to combat so-called relay theft – where thieves boost the signal from a car’s keyless entry fob to get into the vehicle without the key.

The pouches contain a wire mesh, known as a Faraday cage, that can block radio signals from the keyless entry system. However, some thefts have been carried out when the keys were in the pouches.

On cheaper items, it’s possible to damage the mesh through constantly taking the keys in and out. Others don’t have protection applied to all their compartments.

A spokesperson for security firm Thatcham Research told Auto Express that owners should be cautious when shopping for a Faraday pouch. “We have tested a few of the pouches and the ones we’ve assessed have worked, but we can’t guarantee they all will.

“Some pouches have two pockets, for example, only one of which will block signals, while there are so many on the market it’s simply not possible for us to test them all.”

Owners are advised to test a device’s ability to block signals before using it, which they can do by standing next to their car and ensuring it doesn’t unlock.

Some manufacturers are also taking steps to ensure that their cars are safe from relay theft. Ford, for example, recently introduced a ‘sleep mode’ feature to its key fobs – ensuring they can’t be cloned and only work when the driver wants them to.