Faraday bags

What Faraday bags are

A Faraday bag is a small, flexible version of a Faraday cage: an enclosure that blocks electromagnetic fields. How-To Geek describes them as portable cages made of conductive metallic fabric.

• What goes dark: A sealed phone loses cellular, Wi-Fi, Bluetooth and GPS; RFID and NFC cards inside cannot be read.
• Not only phones: Makers also shield key fobs, passports, access cards, tablets and laptops; Mission Darkness says its phone bag also takes a passport or a fob.
• Forensic roots: Investigators use bags with dual paired seams so a seized phone cannot be wiped remotely before it reaches the lab.
• Privacy uses: People use them to stop location tracking, to cut a phone off from networks, and to protect cards and car keys from skimming.
• Who makes them: Mission Darkness, SLNT (formerly Silent Pocket), GoDark, OffGrid and Faraday Defense recur in 2025–2026 reviews.

How they work

An outside electric field moves charges around the conductive shell, and that shift cancels the field inside. A mesh stops a wave only when its openings are much smaller than the wavelength.

• Layers of metal fabric: Mission Darkness lines every interior side with two layers of TitanRF fabric; GoDark uses two or three layers of its own fabric.
• A closed seal: The opening must be shut across its full width: rolled twice under Velcro, rolled and clipped, or folded under a magnetic flap.
• Measured in decibels: Every extra 20 dB cuts the signal’s field strength tenfold; SLNT equates 100 dB with a 100,000:1 reduction.
• Two common standards: MIL-STD-188-125-2 is a military test of shielding against electromagnetic pulse; IEEE 299-2006 is a method for measuring shielding effectiveness.
• Fabric vs finished bag: SLNT notes its lab reports test the shielding material, not the finished sleeve, whose seams and closure also matter.
• Back on when opened: Take the phone out and it starts looking for signal again; calls and messages then come through.

Types

• Phone pouches: Soft bags sized for one phone with a roll-down or fold-over top, such as the Mission Darkness Non-Window bag.
• Window bags: A shielded clear panel lets you see and operate the screen while sealed; Mission Darkness builds them for documenting devices.
• Slim sleeves: Thin sleeves with a magnetic flap and an unshielded outer pocket, such as SLNT’s Faraday Phone Sleeve.
• Dry bags: Waterproof roll-top bags with a shielded main compartment; SLNT rates its dry bags submersible for 30 minutes to 10 feet.
• Key fob pouches: Small pouches or boxes for car keys, sold by SLNT, OffGrid and GoDark.
• Tablet and laptop sizes: The same construction scaled up for larger devices or several phones at once.
• Bags with a Faraday pocket: Slings, backpacks and duffels with one shielded compartment, such as SLNT’s E3 backpack.

What to look for

• Published lab tests: Look for independent results to MIL-STD-188-125-2 or IEEE 299-2006, and check whether they cover the fabric or the finished bag.
• Frequency range: Mission Darkness lists low MHz to 40 GHz and GoDark 200 MHz to 40 GHz, spans that cover cellular including 5G, Wi-Fi, Bluetooth and GPS.
• Fit with the case on: Compare the interior with your phone in its case: SLNT’s Medium sleeve takes 6.65 × 4.5 in; GoDark’s phone bag takes a phone up to 6.75 × 3.25 × 0.5 in.
• A closure you trust: Roll-tops and full-width Velcro seal the whole opening; magnetic flaps are quicker to use one-handed.
• Seams and shell: Dual paired seams, RF-welded seams and water-resistant or IP67-rated outer fabric protect the shielding layer.
• Which pockets shield: Outer slip pockets on many sleeves and bags do not block signals; TruePrepper flags this on SLNT’s dry bag.

On the plane and on the trip

• Through security: TSA allows cell phones in carry-on and checked bags; laptops come out of their bag into a separate bin unless you use TSA PreCheck.
• Passports are covered: U.S. e-passports carry anti-skimming material in the front cover and spine, adopted in 2005 to limit reading of the chip.
• Keyless car fobs: Relay thieves stretch a fob’s signal to open and start a car; ADAC opened and started 629 of 698 keyless cars it tested in 2024.
• Find My goes quiet: Pack Hacker notes Apple’s Find My cannot locate a device inside a shielded pocket, so keep a luggage AirTag outside it.
• Battery drain: NIST notes a phone left on but isolated drains faster, because it raises its signal power to maximum while searching for a network.
• Not the same as airplane mode: NIST notes airplane mode does not always stop services such as GPS; a sealed bag blocks the radios physically.
• Test before you go: Seal the phone and call it from another phone; if it rings or the call connects, the bag or the seal is failing.

Limits and care

• Not always total: In a Purdue field test cited by NIST, most shielding devices tested did not stop network contact in every case; text messages got through most often.
• Why they fail: NIST lists too little attenuation, leaks at seams, and the shield itself acting as an antenna.
• Keep the seal clear: A cable, strap or fold of fabric caught in the closure lets signals pass; Mission Darkness also warns against punctures and wet devices.
• Wear and holes: Worn material or holes let signals in, so How-To Geek advises testing a bag rather than trusting it.
• Cut off on purpose: A sealed phone misses calls and messages and cannot share its location, including in an emergency.
• Fragile fabric: TruePrepper calls bare Faraday fabric fragile and suggests keeping it inside a tougher pouch.

A short history

The shielding effect behind the bag was described in the 1750s. Michael Faraday showed it in 1836, in a room lined with metal foil: the charge stayed on the outside and had no effect inside.

• 1754: Jean-Antoine Nollet publishes an account of the cage effect.
• 1836: Michael Faraday demonstrates it with his foil-lined room.
• October 2005: The State Department adopts e-passports with anti-skimming material in the cover and spine.
• 2010: A Purdue University thesis field-tests phone shielding devices across three large U.S. carriers.
• May 2014: NIST’s mobile forensics guidelines name shielded containers as one of three ways to isolate a seized phone.
• 2015: MOS Equipment, maker of Mission Darkness bags, is established in Santa Barbara, California.
• 2021–2022: Keystone Compliance tests SLNT’s Multishield fabric to MIL-STD-188-125-2 and IEEE 299-2006.