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Faraday Bag: Why You Need One and How to Choose

A mobile phone, car key fob, contactless payment card, or smartwatch – all these devices operate using radio signals. Most of the time this is convenient, but there are situations when you need a device to completely "disappear" from the grid. That is precisely what a Faraday bag is designed for.

In this guide, we explain how it works, when it is useful, what it cannot do, and how to choose and test a Faraday sleeve to ensure it can be relied upon.

How a Faraday Bag Works

A Faraday bag is a pouch or case made from multiple layers of conductive, metalized fabric. When properly sealed, it acts as a Faraday cage: radio frequency signals can neither enter nor leave. Inside the bag, a phone receives no cellular signal, Wi-Fi, Bluetooth, or GPS, while a smart car key cannot communicate with the vehicle.

The critical requirement is complete closure. Even a minute opening or a cable protruding through the closure seam can allow signal leakage.

Why You Need One

Car Key Fobs and Relay Attacks

Vehicles equipped with keyless entry and ignition unlock and start whenever the key fob is in close proximity. The German automobile club ADAC describes how thieves exploit this technology: one relay device is held near the key fob (for instance, by a house front door), while another is positioned next to the car. The key's wireless signal is amplified and relayed across long distances, allowing the vehicle to be unlocked and started within seconds.

A key fob placed inside a securely closed Faraday bag emits no detectable signal, leaving relay devices with nothing to intercept. ADAC highlights additional protection measures:

  • check your vehicle manual to see if keyless entry can be manually deactivated;
  • at home, keep key fobs away from front doors, exterior walls, and windows;
  • when possible, park your car inside a locked garage overnight.

ADAC notes that a protective sleeve is effective only if it blocks all relevant frequencies completely, making verification testing essential. We outline how to perform this test below.

Mobile Phone Privacy

A powered-on mobile phone constantly connects to cellular towers and wireless networks. A Faraday pouch allows you to temporarily sever all wireless connections without powering down the device. This can be desirable during confidential meetings, travel, or whenever you want your device completely off the grid for a period of time.

Cards, Passports, and Backup Electronics

Faraday pouches can also house contactless payment cards, RFID-chipped passports, or backup communications equipment. In an emergency preparedness kit, a shielding pouch keeps documents and devices aggregated in one place, while a waterproof model offers protection against moisture.

What a Faraday Bag Does Not Do

  • Does not wipe or shield internal storage data. Information stored on the phone remains intact, and the device reconnects to networks immediately upon removal.
  • Disables vital incoming alerts. A phone enclosed in a Faraday bag will not receive incoming phone calls or emergency Cell Broadcast warnings. Carefully evaluate when signal blocking is appropriate.
  • Does not replace baseline security practices. Locking vehicle doors, selecting secure parking, and exercising common sense remain vital.

How to Choose a Faraday Bag

Size Based on Intended Use

Key fob pouches fit in a pocket, whereas larger Faraday bags accommodate tablets or multiple devices. Certain phone sleeves feature additional capacity – for instance, according to manufacturer specifications, the Mission Darkness non-window phone pouch can also accommodate a passport, key fob, or payment cards. Select a size tailored to what you intend to store.

Closure Design

The closure mechanism is the primary failure point. Most designs utilize a double-fold system with heavy-duty Velcro or a roll-top opening featuring magnetic or buckle closures. For example, the manufacturer of the Mission Darkness phone pouch recommends folding the opening twice and pressing the Velcro firmly across the full width, ensuring no cables pass through the seal.

Fabric Quality and Testing Standards

Pay attention to the number of shielding fabric layers and whether manufacturer testing certifications are provided. MOS Equipment, maker of Mission Darkness gear, specifies that their shielding fabric is tested to MIL-STD-188-125 and IEEE 299-2006 shielding effectiveness standards.

Environmental Resistance

If carrying a Faraday pouch outdoors or inside a tactical backpack, opt for a weather-resistant or waterproof model. However, note manufacturer warnings that prolonged exposure to immersion or fabric punctures will degrade signal-blocking capabilities. Models featuring MOLLE webbing can be mounted directly to backpacks or tactical vests.

How to Test if Your Faraday Bag Works

  • Call Test. Place a phone inside the bag, seal it completely, and call it from another device. If it rings, the seal is compromised or the shielding fabric is worn.
  • Wireless Connectivity Test. Verify that the enclosed phone is no longer visible to nearby Bluetooth devices or Wi-Fi networks.
  • Key Fob Test. Place your key fob inside the pouch, stand directly beside your vehicle, and attempt to open the door handle. If the car remains locked, the bag is performing correctly.
  • Repeat Regularly. Shielding fabric degrades over time through friction and flex, so re-test your pouch periodically, especially before critical deployment.

In the video below, we test the pouch in practice: the enclosed phone becomes completely unreachable.

Common Mistakes

  • Incompletely closed pouch. Single-folding instead of double-folding or partially fastened Velcro leaves gaps for signal penetration.
  • Charging cables exiting through the closure. Charging a phone inside the bag with a cable routed through the opening ruins shielding effectiveness.
  • Testing only once upon purchase. A new bag may perform flawlessly, but after a year of heavy pack use, shielding material may wear down.
  • Leaving key fobs unshielded "just for a minute." A Faraday pouch provides protection only when the key fob is kept inside consistently when not in active use.
  • Opening the pouch prematurely. Manufacturers advise sealing devices in advance and opening the pouch only where you intend to become reachable again – devices emit signals immediately upon exposure.

Where to Find Them

Our store carries Mission Darkness Faraday bags – including phone pouches and MOLLE utility pouches, as well as waterproof Dry Shield models. View the complete lineup in the "Mission Darkness by MOS" category. Faraday pouches are also included in the "Emergency Preparedness" section alongside field rations and first aid supplies, while our full catalog is accessible here.

Important: A Faraday bag represents just one link in a complete security posture. For comprehensive crisis response training, explore course offerings on the Locked N' Loaded training platform.

Sources

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