How does a Faraday Bag or signal blocker for a keyless car work?

faraday bag

Relay theft is the latest method crooks use to get their hands on our cars. However, a simple way of protecting against it is to buy a Faraday Bag, otherwise known as a car key signal blocker. Find out what they are and whether you should consider buying one here.

How does a keyless car work?

Modern cars with so-called ‘keyless’ technology use a short-range radio signal to deactivate car locking systems when whoever has the key approaches. Once they’re inside the car, the signal from the key then deactivates the car’s immobiliser. This enables whoever has the key to drive off.

How relay theft works

Crooks use a trick known as relay theft to steal keyless cars. One sets up a receiver near to where the key is, say by your front door. When it’s receiving the signal from the key, it bounces this to a colleague with a device near the car. This fools the car into thinking the key is nearby. It unlocks itself and can be started and driven off. The whole process takes less than a minute if done by people who know what they’re doing.

What is a Faraday Bag or signal blocker?

A Faraday Bag is usually a bag lined with metal. You can make your own using a bag and lining it with tin foil. Alternatively, you could put your keys in a metal biscuit tin. This should do the same thing as a Faraday Bag. But proper products are so cheap – often less than £10 – it doesn’t really make sense to create your own.

What a Faraday Bag does

A Faraday Bag or signal blocker stops the key transmitting its signal. Simply put, the bag’s metallic lining prevents the signal escaping. It means no one can hack into the signal and nick your motor.

faraday bag

Make sure you test your signal blocker

Whether you buy a Faraday Bag or make your own, it’s vital to ensure it does what you want it to. Put the car key in it, approach the car and see if the doors unlock. If the key fob’s signal is being blocked they should stay locked. If it works, get into the habit of putting your car key in it as soon as you get home. Also, make sure your spare key lives in one.

Investigate your key

Car makers have got wise to relay theft and some now make keys that have built-in motion sensors. These don’t send out a signal when the key isn’t moving. Others make keys that you can turn off when they’re not required. Check your motor’s user manual to find out if your key has this function.

Think about a physical deterrent

As well as a Faraday Bag, you might consider buying a steering lock. The best ones are difficult for crooks to get off and should be sufficient to ensure they move on to a less well-protected target. Experts advise that you use a lock that covers the entire steering wheel and has been approved by Thatcham. This is the insurance industry’s testing body.