Protecting electronic devices from EMPs

What is an EMP?  EMP stands for Electromagnetic Pulse.  An EMP is typically generated by the detonation of a nuclear weapon.

According to a US Army report from 1994, one single high-altitude detonation has the potential to generate an electromagnetic pulse capable of covering the entire continental United States.

EMPs are not harmful to humans, but have the potential to disrupt and destroy electronic devices such as radios, cell phones, digital cameras, computers, tablet PCs, and e-readers.  Medical devices such as insulin meters and injection systems are also susceptible.  In addition, an EMP will most likely disrupt critical infrastructure.

So how can you protect your devices?  You can spend hundreds of dollars on “EMP protection” bags, boxes, etc, or you can construct your own for a fraction of the cost.

The key is to construct a Faraday Cage.  A Faraday Cage will prevent all electromagnetic signals and pulses from entering or exiting the container.  While many Faraday Cages are made from expensive copper mesh boxes, a smaller Faraday Cage can be made using materials found in the grocery store.

roll of aluminum foil and freezer tape

The EMP protection bag consists of two layers:

  • Conductive Layer
  • Non-Conductive Insulation Layer

Materials you’ll need:

  • Resealable plastic storage bags (vacuum seal bags work best)
  • Heavy duty aluminum foil
  • Freezer Tape

How the bag works (Warning: Science Content!)

  • Since the foil is conductive and creates a closed loop around the contents, any electrical pulse (such as an EMP) or transmission (such as radio waves) coming in contact with the bag will be “channeled” around the bag’s contents (see
  • Any static charge will be unable to reach the bag’s contents due to the non-conductive insulation layer.

First, determine the size of the item you want to protect.  Normally your item will fit inside either a quart or gallon bag.  Purchase the appropriate size bags.  The pictures you see here will illustrate an “emergency” bag which you can keep with you and use to protect your cell phone in an attack, but the procedures for creating a long-term storage bag are nearly identical.

If possible, make sure you are not working in an extremely low or extremely high humidity environment.  Low humidity will result in static electricity, potentially shorting out your electronic device.  High humidity will result in moisture within the electronic device, also capable of shorting out the device.

If this is for a short storage in an “emergency” bag, the item can remain powered on.  For long term storage, power-off the electronic device, as heat will build up inside the bag and possibly damage the device.  Insert the device into the resealable bag.  Then gently squeeze as much air as possible out of the bag while sealing the bag.  If the bag is a vacuum bag, remove all of the air from the bag using a vacuum pump.

Cut a piece of aluminum foil which is larger than the plastic bag by at least 1 inch on each side, and three times the length of the plastic bag.

cut piece of aluminum foil

Place “tape rolls” on one side of the plastic bag, and tape the bag to the aluminum foil so that the bottom of the bag is even with the middle of the foil, as shown.

aluminum foil with tape rolls

Once the bag is taped to the foil on one side, place additional tape rolls on the exposed side of the plastic bag, then carefully fold over the foil.

folded aluminum foil

Fold the sides of the aluminum foil to completely enclose the bag, except for the top opening.  Make sure to create a complete “seal” with the aluminum foil.  If this is for long term storage, go ahead and seal the top using the same method.

sides of aluminum foil folded

sides of aluminum foil fully folded

Instructions for using the emergency bag:

  • Place the item in the emergency bag
  • Seal the plastic bag inside
  • Tightly roll shut the foil

After the aluminum foil has been applied and sealed, the device should be fully protected.  If you’re testing your emergency bag, place your cell phone inside the bag and roll the bag shut.  Now dial your cell phone from another phone.  The cell phone should not have a signal if the protection bag is effective.

About the author:

Ken is a computer security consultant.  You can check out his blog Caffeine Security at

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13 thoughts on “Protecting electronic devices from EMPs”

  1. okay, for the hundreth time….emp might take out the grid, sats, cell towers and anything with LARGE antennae. your little eton radio will still work as will anything not hooked up to grid power at the time. also the study cited was grosly flawed and it would take such a large weapon that nobody but china or russia would afford/ be capable of producing one. we tested this in the military and later in college. it is hugely overblown as a threat. quit freaking out about emp and prep for something you CAN do something about.

  2. Thank you all VERY much for your comments. I wrote this with the hopes of generating a lot of serious discussion on this topic.

    I’ll try to address all of the comments that have been posted so far…

    If it’s conductive, yes, as long as there is an insulation layer as well, to prevent contact transfer to the device.

    I’ve read conflicting information for EMP effects. Some information I’ve read agrees with your statement, that small electronics won’t be affected. Some information says that all electronics will be affected. Having never personally experienced an EMP, I’d rather try to prepare for the worst. With regard to only “China or Russia” being able to produce an EMP capable of covering the United States, the graphic I included was only provided to increase awareness.

    Excellent comments! Ultimately the purpose of this article was to provide instructions for an affordable, homemade EMP protection bag for small electronics, mostly for emergency situations. By no means is this meant to be an all inclusive guide on how to protect large amounts of electronics. I don’t find your ideas excessive at all, but do find them somewhat cost prohibitive.

    More info on Faraday Cages (and an animated graphic) can be found on Wikipedia:
    Yes, this bag only works if you have the device inside. What would prompt you to place your electronics inside the bag? The Emergency Alert System comes to mind. If an attack is imminent, HOPEFULLY, you’ll get advance warning, even if only by a couple minutes.

    @Sundance WMC
    Yes, however, see some of the other comments regarding microwaves.

    My understanding is that for best protection you should leave the microwave unplugged. I’m not sure about the effectiveness of grounding the microwave, because Faraday Cages do not need to be grounded. However it should definitely be removed from the electrical grid.
    Burying the electronics would in theory protect them…but I do not know what the depth would need to be. However, if considering burying electronics, I would recommend a rigid container, not just a simple bag, of your electronics may be crushed.
    I am not an electronics expert, but I am a computer security consultant. There are several parts of computer security (at an enterprise level) from which I have applied my knowledge to write this article:
    1) Continuity of Operations/Disaster Recovery/Disaster Preparedness
    2) Electromagnetic Interference Protection
    3) Signal “leak” protection (Emanation protection aka TEMPEST )

    Computer security is not just about viruses and patches. Every aspect is considered, including physical risks from natural and man-made threats.


  3. Just an FYI: for a Faraday cage to be effective against a given frequency of electromagnetic radiation, the gaps in it MUST be smaller than the corresponding wavelength. An upper atmospheric detonation of a nuclear device basically produces an EMP (actually 3 distinct pulses) that covers a huge range of the EM spectrum.

    “So,” you say, “what the hell did any of that mean?” Practically speaking, it means that a microwave will protect against cell phone signals, but in the event of a nuclear EMP, you won’t get a whole lot of protection from it. It’s that grate with the little holes that lets you watch your food spin. Also, it means that a foil-wrapped bag may be the best you can do if you’re out and about, but when it comes to stuff in your home that’s being stored protected, you can and should do better.

    At least use multiple layers of bag, foil, bag, foil, etc. If you can, place that package in a metal cabinet (without allowing contact between the metal of the package and the cabinet). If you can, place the metal cabinet underground. Under a couple feet of soil or concrete would be best, but if that’s not an option, a basement is better than nothing. Make sure it won’t flood, though, or you’ll have other problems with your electronics.

    Sorry for the rant; I’m sure anybody reading this is thinking that’s all pretty excessive. It’s just bugs me when I see preppers thinking they’re set when they’re actually wildly exposed to the very danger they’re combating.

  4. My only question about these cages is how to get them to really work??? I mean, an EMP attack can strike without warning so unless you have your electronics wraped up in them 24-7 how would they be effective? Please explain – perhaps I am missing something. Thanks much!

  5. as I understand it, a microwave oven makes a good faraday cage. If you have one that no longer works, it can be used to store electronics that will fit inside.

  6. I’ve read that just using a microwave will not work just by itself. Also read controversies about whether to ground the microwave (the one I believe is not to ground it). Also what about burying electronics underground with the bags sealed from moisture, depth level? Are you an electronics expert? What say you about these statements?.

  7. I think the more important part of the lesson is the fact that we have become to dependent on electronics. If there is an EMP event the last thing I am worried about is if my cell phone works or not. As for communications devices those I would worry about more than anything else. Automotive parts that are susceptible to an EMP would also be my first order of business. Household generators and important medical devices would be right up there with the auto parts. Having a working iPad is about the last worry on my mind. A working lap top would be another device that I would plan to protect so that valuable info can be transferred over to the laptop from thumb-drives to be stored. Who are you going to call if all the network towers are fried anyway? An iPad is just a big cell phone for the most part and will be all but useless unless you already have your stuff on it. I guess my point is do what ever is necessary to wean your self off of having so many electronics devices that are so vital. If you are not able to send an e-mail there is always the post office so just write a letter or better yet go over and see the person you need to communicate with. This is what they did before all this electronics crap came around anyway.

  8. A cheap way to protect yourself. Pennies. Glue 2 layers of pennies to the inside of a metal box or trunk. Copper foil, flashing or mesh cost a fortune. 2 Layers of pennies over lapped will do the trick.

  9. Jennifer – the old saying among preppers is – One is NONE, Two is ONE. Just having ONE radio is having NO radio. But don’t go overboard when practicing the one is none, two is one method. Some common sense is required.

    A electrical engineer friend of mine made this comment to me when I asked about EMP’s. His comment was “Always have spares tucked away because you’ll NEVER know when a EMP will hit.” Then he said bluntly – if it’s a radio device – ie cell phone, radio, short wave transceiver – best way to see if it will conduct EMP and ruin the device is to put it into the storage device – mylar bag, ammo can, faraday box etc – and if you can still hear it broadcasting (radio, walkie talkies, CB) then it WILL not be EMP resistant. Pretty basic hugh? I currently have a spare CB, batt operated radio, 2m handheld & mobile units, FRS radios wrapped in mylar bags I got from the LDS storehouse, wrapped in a layer of bubble wrap, then placed into a large 20mm ammo can. Personally, I only do this with my communications gear and with a spare older laptop I picked up really cheap.

  10. @Ken
    Trust me, I know about cost prohibitive. Having just recently graduated college, I’ve got plenty of student debt to go with my tight budget. Sometimes it feels like there’s no way I’ll ever be stable enough to be able to prep the way I want. On the plus side, I learned neat stuff like the nature of EMP while studying to be an electrical engineer, and eventually I ought to be able to make some money.

    I just meant if someone had a spare ammo can and a filing cabinet for papers, it’d be a good idea to layer one’s protection. Obviously, the off-grid, self-sufficient, electromagnetically-isolated underground bunker would be nice, but who the heck has that kind of money!? lol

    In any case, good write-up with good illustrations!

  11. @Badvoodoodaddy
    I’m glad you brought this up! Why would you want to protect your cell phone from an EMP?
    Personally, I have an Android smart phone. The last thing I’m worried about is being able to place a call. On this phone is a rather large collection of PDF files with survival documentation. I have tried to memorize a lot of this documentation, but I would really like to have this information accessible in a disaster.


  12. There are so many good websites that talk about the topic of EMP. One that I have grown to love is actually a radio blog show. It’s at Dr. Peter Vincent Pry and Prof Cindy Ayers is going to be on the show on Wednesday the 28th at Noon to have a 2011 in review show. They are going to be covering huge topics like nuclear EMP-related events and other threats to our nation and way of life. They’re also going to talk about mainstream national security current events and discuss unclassified CIA, National Security Agency (NSA), and other intelligence agencies matters. It’s going to be a great show to listen to, I’m looking forward to it. Here’s the link for more information and to listen to it tomorrow:


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