What is a Faraday bag and what do they do?

In this guide, we will define a Faraday bag, explain how it works - and why you may need one. We’ll also cover alternative security measures for keyless car owners. Keyless entry is a convenient feature that allows you to unlock your car without the use of a key or button. If you have a car with this technology, you won’t have to worry about scrambling for your car keys whilst carrying your weekly shop!

Keyless entry systems work by using low-frequency signals which are transmitted between the car and the key, allowing short-range sensors to unlock the car. Sometimes, these systems can even start the car without the use of a key (so long as the sensors pick up on its presence within the vehicle).

However, keyless entry technology does present extra car security challenges – and may leave your car more vulnerable to theft. Any car with keyless entry technology is susceptible to ‘relay theft’ (where thieves use the keyless system against itself to trick the car into thinking the owner’s wireless fob is nearby).

To mitigate this problem, many drivers invest in a Faraday bag – a specialised device designed to block prospective thieves’ attempts to gain entry.

In this guide, we will define a Faraday bag, explain how it works - and why you may need one. We’ll also cover alternative security measures for keyless car owners.

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What is a Faraday bag?

A Faraday bag is a specialised bag, pouch or box designed to block the electromagnetic signals emitted by a car key stored within it, providing a shield against electronic communication - and preventing thieves from gaining access to the key.

Faraday bags are typically made from layered, metallic fabric, featuring materials such as copper, aluminium and static dissipative polyester.

What does a Faraday bag do?

Faraday bags work by diverting the path of an electromagnetic field, preventing waves from reaching and interacting with anything within the bag. (They’re essentially much smaller, modernised versions of a Faraday cage.)

Whenever electromagnetic waves are headed for (or emitted by) an item inside the bag (in this case, your car key), they are conducted throughout the fabric, diverting the energy and blocking signals from reaching it.

Why do you need a Faraday bag?

As keyless entry systems grow in popularity, car thieves are continually developing new ways to intercept them.

‘Relay theft’ is one of the most common methods used by keyless entry car thieves. This approach sees a team of criminals use electronic tools to pick up and amplify the electromagnetic transmissions between the key and the car, allowing them to unlock it from further away.

Keeping your car key in a Faraday bag protects you from this type of theft, along with any other methods that rely on the use of electronic tools to intercept electromagnetic transmissions.

How much does a Faraday bag cost?

Faraday bags, pouches and boxes are sold by a vast range of retailers and can be purchased for as little as £5, making them a very affordable solution to what is potentially a very serious problem.

Are all Faraday bags of similar quality?

Faraday bags vary in price. Many premium models do have a higher build quality and utilise higher quality materials. However, any properly made Faraday bag should be effective, so you don’t necessarily need to break the bank.

Are Faraday bags legal?

Yes, Faraday bags are completely legal to own and use.

What can you use instead of a Faraday bag?

Want to create a DIY Faraday bag rather than purchasing one? Here are two alternatives that only require a few common household materials:

The aluminium foil method

For this method, you’ll need aluminium foil and plastic cling film:
- Wrap your car key in a layer of cling film. (If your car key has any exposed sharp edges, you might want to wrap it in a thin layer of fabric first.)
- Wrap your car key in a layer of aluminium foil. Make sure there are no holes, gaps or tears in the foil, or it will be ineffective.
- Repeat this process, alternating between aluminium foil and plastic cling film layers as you go, whilst continuing to make sure there are no tears, holes or gaps. You’ll need at least three layers of both materials for your DIY Faraday pouch to be effective.
The metal container method

For this method, you’ll need plastic cling film and a metal container. (Steel, aluminium and other similar materials should all work effectively.) Just make sure that the container has a tightly closing lid.
- Line the inside of your metal container with the cling film. (Make sure there are no holes or tears in the plastic wrap.)
- Wrap your car key in a layer of cling film. You can alternate cling film layers with aluminium foil layers for optimal protection.
- Place your car key inside the metal container and ensure it is properly closed.

Are Faraday bags worth it?

Given their low price and wide availability, if your car uses keyless entry, you should certainly consider protecting yourself from car theft with a Faraday bag. With options starting from around £5, it’s a small price to pay for your peace of mind.