Guide # Do Faraday bags work? Yes, if the bag is well made and fully sealed. A worn or half-closed bag can let signals through, so test yours at home. This guide shows how, and gives the honest answer about EMP. By [The OffGridOne team \[\[OWNER: FOUNDER_NAMES_FOR_ABOUT_PAGE\]\]](https://www.offgridone.com/about). Last updated November 9, 2026 Yes, a Faraday bag can work. A well made bag, sealed all the way, blocks radio signals such as cell and Wi-Fi from reaching the phone inside. But quality varies a lot, and the seal is the weak spot, so test yours. The harder question is EMP. We give the honest answer below, and it is not a promise. ## What is a Faraday bag? A Faraday bag is a pouch lined with conductive material that blocks radio signals while it is sealed. Police use them to keep seized phones from connecting to any network. Many people use them to keep a phone off the air in storage. The Justice Department's guide for first responders says these bags are used "to prevent mobile phones and devices from connecting to communication signals." It tells officers to wrap seized phones in shielding material so they cannot receive a call or text that might change the evidence ([NIJ guide](https://www.ojp.gov/pdffiles1/nij/219941.pdf)). The federal EMP guidelines call Faraday bags the most basic type of shielding. They are designed mainly for small items such as phones, key fobs and tablets ([DHS EMP guidelines](https://www.cisa.gov/sites/default/files/publications/19_0307_CISA_EMP-Protection-Resilience-Guidelines.pdf)). ## Do Faraday bags work? A good one does, but not every bag does. A federal report found that most shielding products in an older university test did not block the network in every case. Quality, size and build vary greatly. Test any bag you plan to rely on. NIST reported on a university test from 2010. It said most of the shielding devices tested did not stop network communication in all cases. Texts leaked in most often, followed by voice calls ([NIST 800-101](https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-101r1.pdf)). NIST also notes that some of those products have been improved since. Its advice to investigators is simple: test your own products to make sure they work before use ([NIST 800-101](https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-101r1.pdf)). The DHS guidelines agree that bag size, build and protection level "can vary greatly" ([DHS EMP guidelines](https://www.cisa.gov/sites/default/files/publications/19_0307_CISA_EMP-Protection-Resilience-Guidelines.pdf)). That is why a home test matters more than a label. ## How do I test a Faraday bag at home? Seal a working phone in the bag, then call it from another phone. If it rings or buzzes, the bag leaks. If the call goes to voicemail, the bag blocked that signal. Repeat for texts and for every way you close the bag. 1. Charge the phone and make sure it works. Call it once with no bag, to confirm it rings. 2. Turn the ringer up. Place the phone in the bag and close it the way the maker says, every fold and every seam. 3. From another phone, call the sealed phone. Let it ring out. A call that rolls to voicemail is a pass. 4. Send a text to the sealed phone. Wait a few minutes, then open the bag and check. Texts leaked most often in the NIST review ([NIST 800-101](https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-101r1.pdf)). 5. Turn Wi-Fi and Bluetooth on, and check them the same way if you can. 6. Repeat with the bag folded, rolled and flipped. Test again after months in storage. Know what this test proves. It shows the bag blocks the signals you tried, on the day you tried them. It does not show that the bag would protect against an EMP. Those are different questions. ## Do Faraday bags protect electronics from an EMP? No one can promise that. We found no official test of a modern smartphone against an EMP. Federal guidelines call small electronics fairly resilient and say a Faraday cage for them is of secondary importance. The bigger risk is to power lines and networks. DHS defines an electromagnetic pulse as a burst of energy from a nuclear explosion in the atmosphere. It could damage power lines, telecommunications and electronics ([DHS, EMP](https://www.dhs.gov/science-and-technology/electromagnetic-pulse-empgeomagnetic-disturbance)). The federal EMP guidelines say small electronics without long cables, such as cell phones, are "relatively resilient" to EMP, while the networks behind them are not. They add that small devices can still be disrupted, especially if turned on or charging at the time ([DHS EMP guidelines](https://www.cisa.gov/sites/default/files/publications/19_0307_CISA_EMP-Protection-Resilience-Guidelines.pdf)). The same guidelines still list Faraday containers for spare electronics at their lowest-cost level ([DHS EMP guidelines](https://www.cisa.gov/sites/default/files/publications/19_0307_CISA_EMP-Protection-Resilience-Guidelines.pdf)). So a bag is a cheap extra layer. It is not proven protection, and no bag should come with an EMP promise. Space weather is a related risk. NOAA rates solar storms from G1 to G5, and at G5 some power grids may collapse or black out ([NOAA scales](https://www.swpc.noaa.gov/noaa-scales-explanation)). Ready.gov says severe space weather can disrupt communications and GPS ([Ready.gov, space weather](https://www.ready.gov/space-weather)). A bag does not change that. It is one small part of a plan. ## Why do Faraday bags stop working? Mostly at the seal. NIST names three causes: not enough shielding material, leaks at seams, or the shield acting like an antenna. DHS says the closing method is often the main leak point. Look for a bag tested as a whole. The DHS guidelines warn that many bags sold as Faraday bags are made for evidence collection and may give only static protection. They also say a plain Mylar food bag provides little protection ([DHS EMP guidelines](https://www.cisa.gov/sites/default/files/publications/19_0307_CISA_EMP-Protection-Resilience-Guidelines.pdf)). Any tear, hole or half-closed fold is a gap. Check the bag now and then, and retest it after any damage. ## Can I keep my phone in a Faraday bag for months? Yes, but a phone left on inside will keep searching for a signal and drain its battery. Switch it off, store it about half charged in a cool, dry place, and top it up every few months. The FCC and FEMA say that a phone with no signal bars drains faster as it searches, and turning it off prevents that ([FCC tips](https://www.fcc.gov/emergency)). The National Park Service gives the same warning ([NPS Hike Smart](https://www.nps.gov/articles/hiking-safety.htm)). For storage, Apple advises keeping a device half charged and powered down in a cool, moisture-free place, and charging to 50% every six months ([Apple, batteries](https://www.apple.com/batteries/maximizing-performance/)). Samsung advises 50 to 70% and a charge every 3 to 6 months ([Samsung, battery](https://www.samsung.com/us/support/galaxy-battery/care-and-maintenance/)). Our [long-term phone storage guide](https://www.offgridone.com/guides/how-to-store-a-phone-long-term) covers the full routine. A note on OffGridOne A Faraday bag is included with every order of the OffGridOne offline AI survival device. Bag details and any supplier test data: \[\[OWNER: FARADAY_BAG]]. We make no EMP promise. Seal a working phone in the bag and call it, as shown above. [See the Faraday bag page](https://www.offgridone.com/faraday-bag). ## Sources 1. U.S. Department of Justice, National Institute of Justice. [Electronic Crime Scene Investigation: A Guide for First Responders, Second Edition](https://www.ojp.gov/pdffiles1/nij/219941.pdf). Published April 1, 2008. Checked November 9, 2026. 2. DHS National Coordinating Center for Communications. [Electromagnetic Pulse (EMP) Protection and Resilience Guidelines for Critical Infrastructure and Equipment, Version 2.2](https://www.cisa.gov/sites/default/files/publications/19_0307_CISA_EMP-Protection-Resilience-Guidelines.pdf). Published February 5, 2019. Checked November 9, 2026. 3. NIST. [Guidelines on Mobile Device Forensics, SP 800-101 Rev. 1](https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-101r1.pdf). Published May 1, 2014. Checked November 9, 2026. 4. DHS Science and Technology Directorate. [Electromagnetic Pulse (EMP)/Geomagnetic Disturbance](https://www.dhs.gov/science-and-technology/electromagnetic-pulse-empgeomagnetic-disturbance). Published January 30, 2026. Checked November 9, 2026. 5. NOAA Space Weather Prediction Center. [NOAA Space Weather Scales](https://www.swpc.noaa.gov/noaa-scales-explanation). Checked November 9, 2026. 6. Ready.gov (FEMA). [Space Weather](https://www.ready.gov/space-weather). Published March 5, 2026. Checked November 9, 2026. 7. FCC and FEMA. [Emergency Communications Tips](https://www.fcc.gov/emergency). Published May 1, 2026. Checked November 9, 2026. 8. National Park Service. [Hike Smart](https://www.nps.gov/articles/hiking-safety.htm). Published June 13, 2024. Checked November 9, 2026. 9. Apple. [Batteries: Maximizing Performance](https://www.apple.com/batteries/maximizing-performance/). Checked November 9, 2026. 10. Samsung. [Galaxy Battery: Care and Maintenance](https://www.samsung.com/us/support/galaxy-battery/care-and-maintenance/). Checked November 9, 2026. About OffGridOne OffGridOne is an offline AI survival device: a rugged device with an AI that answers with no internet and no cell service. A Faraday bag is included with every order. [See the device](https://www.offgridone.com/offline-ai-survival-device) ## Keep reading - [OffGridOne offline AI survival device: Price, what is in the box, shipping, returns and warranty, next to the buy button.](https://www.offgridone.com/offline-ai-survival-device) - [Faraday bag: Every OffGridOne ships with a Faraday bag for the device. What it blocks, what it does not, how to test it, and how to store the device so it is ready.](https://www.offgridone.com/faraday-bag) - [How to store a phone long term: Store a backup phone partly charged, powered off, cool and dry, and top it up on a schedule. The routine, with phone makers' own battery guidance.](https://www.offgridone.com/guides/how-to-store-a-phone-long-term) - [OffGridOne FAQ: Plain answers to the questions people ask before they buy.](https://www.offgridone.com/faq) --- Canonical page: https://www.offgridone.com/guides/do-faraday-bags-work