What is a Faraday Bag and Should You Use One?

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 do Faraday bags work?

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

These cages work by surrounding an object with a conductive metal mesh. When an electromagnetic field meets the cage, it conducts itself around the objects inside. If you are struck by lightning while inside a Faraday cage, you will be completely unharmed as the energy is deflected around you. Ideally, the cage should be made of continuous metal, but that’s 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 want to block.

Going back to Faraday bags, they are made of a conductive wire mesh that blocks signals from reaching what’s inside. You can buy these bags almost 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 that its Wi-Fi, Bluetooth, and other internal radios work via a software switch, not a physical kill switch. In other words, you have no way of knowing that your device isn’t actually sending or receiving data when you put it in airplane mode or turn off Wi-Fi.

That’s one of the reasons Faraday bags are useful. When you want to make sure your devices don’t get in the way of Wi-Fi access points, cell towers, RFID readers, and Bluetooth beacons, you can use a bag to hide them. If you want to temporarily go incognito, wearing a Faraday bag is better than leaving your phone behind.

Another great reason to use a Faraday bag is to protect your RFID devices from theft. You can put access cards, RFID car fobs and anything else that can be copied within short distances inside the bag. This will frustrate criminals trying to steal your data using skimming methods.

Making sure your Faraday bag works

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

This makes it important to test your bag when you first receive it and periodically for as long as you have it. The easiest way to see if the bag works is to put your phone in it and then try calling from another device. If the call goes through, then you know the bag is malfunctioning. 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 manufacturer of Faraday bags, also has an Android app designed for testing bags. After running the test, you’ll get a report showing exactly how much the application was able (or not) to get through the shield.

Should you use a Faraday bag?

Assuming you have a job board you can trust to get your work done, there’s no harm in adding it to your personal privacy arsenal. The ability to disconnect your devices from wireless communication is a powerful option when, for example, you don’t want Google to know that you’re visiting certain places. If you suspect your phone has been compromised by serious tracking malware such as a rootkit, these bags provide a non-technical way to address the problem immediately. Even hackers can’t hack the laws of physics, after all.

There are drawbacks to using a Faraday bag. If you forget your things in the bag, you will miss calls and emails. If you lose your bag, you can’t use services like Find My to track your things. Functional location sharing features also offer a level of security in emergency situations. However, use yours correctly and you’ll be able to jump in and out of the network at will without giving up your smartphone. Now you just have to deal with public facial recognition.

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