Test Your
Faraday Bag
A Faraday bag blocks radio signals with a lining of metal fabric. It only works when it is fully sealed and undamaged, so test it when it arrives and again every few months.
Seal it completely. One loose fold or small gap lets signal straight through. Close it the way the maker shows, every time.
How It Works
Radio signals cannot pass through an unbroken shell of metal. The bag is that shell, made flexible.
A Metal Skin
Inside the outer fabric is a lining woven with metal. Sealed, it wraps your device on every side, and signals stop at the lining.
What It Blocks
- Mobile calls, texts and data
- Wi-Fi, Bluetooth and GPS
- Keyless car key and tap-and-go card signals
Why the Seal Matters
A gap in the closure or a tear in the lining is a hole in the shell. Signal finds it. A bag left half open blocks almost nothing.
Seal It Properly
Most bags that fail a test were simply not closed all the way.
How to Close It
- 1 Push the device right down inside, well below the fold line
- 2 Flatten the opening and squeeze the air out
- 3 Fold or roll the top over tightly, at least twice, or as many times as the maker says
- 4 Press the fastener shut along its full width
Other Closures
- Boxes: shut the lid fully and do up the latch. Nothing may poke out
- Small key pouches often have two pockets. Only the lined inner pocket blocks signal
- Don't overfill it. If it cannot close flat, it is not sealed
The Phone Test
Two phones and two minutes. Do it at home, where your signal is at its usual strength.
Call It
- 1 Turn the ringer up, and leave Wi-Fi and Bluetooth on
- 2 Seal the phone in the bag
- 3 Wait about a minute
- 4 Call it from another phone
- 5 Take it out. It should take a moment to find its network again
Reading the Result
- Pass: the phone stays silent and your call goes to voicemail or does not connect
- Fail: it rings, buzzes or lights up with the call
- The missed call may show up once it is back on the network. That is normal
The Bluetooth Check
- Play music from the phone to a Bluetooth speaker or earbuds
- Seal the phone in the bag
- The music should cut out within a few seconds and stay off
Car Keys and Cards
Test the thing you actually bought the bag to protect.
Keyless Car Key
- 1 Lock the car and seal the key in the pouch or box
- 2 Walk up to the car holding it
- 3 Try the door handle. The car should stay locked
- 4 Take the key out and check the car opens as normal
Tap-and-Go Cards
- Put the card in the pouch or sleeve
- Hold it to a card reader, at a self-checkout for example
- The reader should not see the card
Building and gate access fobs use a different, lower frequency that is harder to block. Test yours before you assume it is covered.
If It Fails
Work through these before you give up on it.
Check, Then Retest
- 1 Close it again with one more fold, pressed flat along the whole width
- 2 Make sure the device sits fully below the fold
- 3 Look inside for holes, worn creases or a seam that has lifted
- 4 Test again
Still Failing
- Stop relying on it
- If it is new, contact the seller. If you bought it from us, get in touch
- An old bag with a worn lining has done its time. Replace it
Care
The metal lining is thin. Sharp creases and sharp objects are what wear it out.
Do
- Store it flat or loosely rolled
- Slide keys and tools in gently, points away from the lining
- Wipe it clean with a damp cloth
- Retest every few months, and after any rough trip
Don't
- Don't machine wash or tumble dry it
- Don't fold the body of the bag into sharp creases, or sit on it
- Don't stuff it so full that the top cannot fold properly
- Don't seal in a phone that is switched on for long. It hunts for signal and flattens its battery. Turn it off first
Know the Limits
Passing a home test is a good sign. It is not a laboratory rating.
What a Home Test Shows
- It shows the bag stops everyday signals: phone, Wi-Fi, Bluetooth, car key
- It does not measure how strong the shielding is
- No home test can prove protection against a solar storm or an electromagnetic pulse
For Grid-Down Storage
- Seal in the spares you would want afterwards: a small radio, a torch, a power bank and a USB stick of documents
- For extra margin, put a small sealed bag inside a larger sealed bag
- Leave them in there. Gear only counts as protected if it is inside when it happens
Shielded and Ready
Faraday dry bags, pouches, key boxes and card protection.
More From the Survival Hub
This guide is general information only. Faraday products differ, so always follow the instructions that came with yours. A home test is a basic check and does not certify a product's shielding. In a life-threatening emergency, call Triple Zero (000).