What is a Faraday bag and should you use one?

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Faraday bags use the same principles as a Faraday cage to prevent wireless signals from leaving or reaching your devices. So what are the reasons for using one, and how is it different from turning off the device or using airplane mode?

How Faraday Bags Work

Faraday bags are basically portable and flexible Faraday cages. A Faraday cage, named after scientist Michael Faraday, blocks electromagnetic waves from reaching anything inside.

These cages work by surrounding an object with a conductive wire mesh. When an electromagnetic field encounters the cage, it is conducted around the objects inside. If you were struck by lightning while inside a Faraday cage, you would be completely unharmed as the energy is diverted around you. Ideally, the cage should be continuous metal, but this is often too expensive or impractical. A mesh works just as well, as long as the holes in the mesh are sufficiently smaller than the wavelength of the signals you wish to block.

Mission Darkness Windowless Faraday Bag

The Mission Darkness Bag is an affordable and effective way to protect your RFID devices from attack or temporarily block your phone’s radios to prevent tracking or data theft.

Going back to Faraday bags, these are made of a conductive metal fabric that blocks signals from reaching anything inside. You can buy these bags just about anywhere these days, so are they worth your time and money?

Why use a Faraday bag?

Consider that your smartphone probably doesn’t have a removable battery, and your Wi-Fi, Bluetooth, and other internal radios are operated by a software switch, not a physical kill-switch. In other words, you have no way of knowing that your device isn’t really sending or receiving data when you put it on airplane mode or turn off Wi-Fi.

This is one of the reasons Faraday bags are useful. When you want to make sure your devices don’t shake hands with Wi-Fi hotspots, cell towers, RFID readers, and Bluetooth beacons, you can use a bag to hide them. If you want to temporarily go incognito, it’s better to use a Faraday bag than to leave your phone behind.

Another good reason to use a Faraday bag is to protect your RFID devices from skimming. You can put access cards, RFID car key fobs and anything that can be copied at short distance inside the bag. This will thwart criminals who try to steal your data using skimming methods.

Making Sure Your Faraday Bag Works

Faraday bags are effective, but they can be compromised. If the bag develops holes or the material wears out, it may begin to leak signals. Some Faraday bags just aren’t good out of the box.

It is therefore important to test your bag when you first receive it and periodically during your time with it. The easiest way to see if the bag works is to put your phone in it and then try calling it from another device. If the call goes through, you know the bag isn’t working properly. The same goes for RFID cards. If the card still works when sealed in the bag, that bag is not working properly.

Mission Darkness, a maker of Faraday bags, also has an Android app designed to test the bags. After running the test, you’ll get a report showing exactly what the app was able (or couldn’t) get through the shield.

Should You Use a Faraday Bag?

Assuming you have a work bag that you can trust to do its job, there’s nothing wrong with adding it to your personal privacy arsenal. The ability to mute your devices from wireless communication is a powerful option when, for example, you don’t want Google to know you’re visiting certain locations. If you think your phone has been compromised by serious tracking malware, like a rootkit, these bags provide a non-technical way to deal with the problem immediately. Even hackers can’t hack the laws of physics, after all.

There are downsides to using a Faraday bag. If you forget your stuff in the bag, you’ll miss calls and emails. If you lose your bag, you can’t use services like Find My to find your stuff. Functional position sharing features also provide a level of security in emergency situations. Use yours correctly, though, and you can swipe on and off the grid at will without giving up your smartphone. Now all you have to do is take care of the public facial recognition.

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