Faraday bag vs phone case: which one do you actually need?

"Can't I just get a Faraday phone case?" comes up a lot. It's a reasonable thing to ask. You already carry your phone in a case all day, so why add another thing to your pocket?

The trouble is that "Faraday", "shielding" and "anti-radiation" get printed on all sorts of products that work in completely different ways. Some of them do nothing to the signal at all. So before comparing anything, it helps to sort out what we're actually talking about.

Three different things get called a "case"

1. A regular phone case

Silicone, plastic, leather, rugged armor, whatever you like. It's there to stop cracked screens and scratches. It has no real effect on your signal. Your phone makes calls, uses GPS and connects to Wi-Fi exactly as it would without it.

2. A "radiation-blocking" or flip case with a shielded flap

These usually look like a wallet case with a front cover lined with shielding fabric. The idea is that the flap sits between the phone and your head or body. The phone still works normally while it's in the case, and that's the giveaway: if it can still make calls, the signal is still getting in and out.

3. A Faraday sleeve or bag

A pouch lined with shielding fabric that closes completely around the phone, usually with a roll-top or fold-over seal. Some are shaped like a phone sleeve, which is why people sometimes call them cases. Once it's sealed, the phone is fully offline. You can't use it until you take it out.

Side by side

Why a case can't do what a bag does

Blocking radio signals comes down to one rule: the shielding has to surround the device completely. We go into the physics in how Faraday bags work, but the short version is that any opening that's large compared with the signal's wavelength lets the signal through. Phone signals have wavelengths of a few centimeters to a few tens of centimeters. An uncovered back, an open edge or the gap around a camera cutout is plenty.

Signals also don't come from one direction. They bounce off walls, cars and buildings and reach your phone from all around, so shielding one side barely changes what the phone receives.

There's also a catch that makes partial shielding worse than it sounds. When a phone's reception gets weaker, it turns up its transmit power to stay connected. The US Federal Trade Commission has pointed this out in its consumer advice on phone "radiation shields": products that cover only part of a phone can interfere with the signal and make the phone work harder, which may actually increase what it emits.

If your phone can still make a call, the signal is still getting in and out. It really is that simple.

When a regular case is all you need

For most of the day, a normal case is the right thing to have on your phone. You want to take calls, use maps, pay with your phone and get notifications. A case protects all of that from the occasional drop, and none of it works inside a Faraday bag anyway.

If your worry is a cracked screen, a case is the answer. If your worry is being tracked, reached or scanned, a case doesn't touch that.

When a Faraday bag makes sense

A Faraday bag is for the times you want your phone, or something else wireless, to go completely quiet. A few common ones:

• Private meetings and conversations, where you want to know for certain that nothing is transmitting or listening.
• Travel, when you'd rather your location wasn't being logged, or you want to keep a work phone off the network between trips.
• Car keys at home. A keyless fob in a pouch by the front door stops relay theft. A phone case obviously can't help with this.
• Cards and passports, to stop contactless chips being read without you knowing.
• Storing backups, like a spare phone, a hardware crypto wallet or a drive you want kept fully offline.
• A proper break. Sometimes you just want a few hours where the phone can't buzz, ping or ring. Sealing it in a bag is harder to cheat on than turning on Do Not Disturb.

Can you use both?

Yes, and most people do. Keep your usual case on for everyday protection, and put the phone, case and all, into a Faraday sleeve when you want it offline.

The one thing to check is size. A phone in a thick rugged case can be noticeably bigger than the phone on its own, and a Faraday bag only works if the closure can be folded or rolled all the way. If you have to force the top shut, get the next size up. It's also why we make phone-sized bags as well as larger ones for laptops.

How to spot a "Faraday case" that isn't one

• You can use the phone while it's in it. Then it isn't blocking the signal. A real Faraday enclosure and a working phone can't happen at the same time.
• It only covers one side. A flap, a sticker or a card-sized insert can't shield a phone, however it's described.
• There's no proper closure. Magnetic snaps and loose flaps leave gaps along the edges. Look for a roll-top or a fold-over seal.
• It says "blocks 99% of radiation" and nothing else. As we explain in the other guide, 99% is only 20 dB, which often isn't enough to stop a phone ringing.

The easiest check is the same one we recommend for any Faraday product: seal the phone in, wait 30 seconds and call it from another phone. If it rings, it isn't doing the job.