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Tech & privacyUpdated November 20262 min readBy Plainbench editorial team

Faraday bags explained: what they block and who needs one

A Faraday bag blocks wireless signals to whatever is inside. Here is what that covers, what to check, and how to test one at home.

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Hands holding a smartphone in the dark

What a Faraday bag blocks

A Faraday bag is a pouch lined with layers of conductive fabric. When it is fully closed, it stops radio signals from reaching the device inside: cellular, GPS, Wi-Fi, Bluetooth, NFC and the signal from a car key fob.

It only works when sealed. An open flap or a worn lining lets signals through.

Who uses one

Car ownersKeyless-entry fobs stored in a sealed pouch cannot be read by relay devices from outside the house.
TravelersKeep passports, cards and spare phones from broadcasting or being scanned.
Privacy-minded usersTake a phone fully off the network without powering it down, for example in meetings.

What to check before you buy

FeatureWhy it matters
ClosureRoll-top or double-fold closures seal more reliably than a single flap.
Lining layersMore layers of shielding fabric hold up better as the bag wears.
SizeKey fob, phone, tablet/laptop or bag-sized. Check inner dimensions, not outer.
Testing claimsLook for brands that publish independent lab test results, not just a "blocks everything" claim.

How to test it at home

  1. Put your phone inside and close the bag fully.
  2. Call it from another phone. It should go straight to voicemail.
  3. For a key fob, seal it inside and walk to the car. The doors should not unlock.

Repeat the test every few months. Linings wear out with folding and use.

Who this is for

Good fit if you…

  • use a keyless-entry car
  • travel with sensitive cards, passports or devices
  • want a phone off the network without powering it down

Skip it if you…

  • expect it to protect against every threat (it only blocks radio signals while sealed)
  • need regular calls or navigation while the device is stored

FAQ

Will a Faraday bag drain my battery?

Devices may search harder for a signal while sealed. For long storage, switch the device to airplane mode or power it off.

Does aluminum foil work the same?

Foil can block signals if wrapped perfectly, but it tears easily and is hard to seal reliably. Purpose-made bags are easier to use and test.

How long does a Faraday bag last?

It depends on use. Folding and wear can crack the lining, which is why regular at-home testing matters.

Is it legal to use one?

Yes. Faraday bags are passive pouches and do not jam or interfere with other people's signals.

Written by

Plainbench editorial team

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