How to Build a Simple Faraday Cage for EMP Survival

Avatar for Jodie Weston Jodie Weston  |  Updated: June 6, 2022
How to Build a Simple Faraday Cage for EMP Survival

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Of all of the reasons to prepare, one that we all need to take seriously is the possibility of a catastrophic EMP, or electromagnetic pulse. This is a frequent topic in many post-apocalyptic novels and something that most of us are aware of, even if we do not completely understand the science.

How to Build a Simple Faraday Cage for EMP Survival - Backdoor Survival

As I wrote way back when in the article Prepping for an EMP and Solar Flares:

To be blunt about it, an EMP, if large enough, would affect the entire planet.  In an instant, civilization as we know it would change as we get swept backward in time by a century or two.

Understanding the risks of an EMP goes hand in hand with threats of a cyber-attack since there is a cause and effect relationship between the two.  In this article I want to accomplish a few things:

Explain EMPs and the risks in simple, easy-to-understand language
Give you instructions to build a simple Faraday cage to protect your electronic equipment.
Provide a list of items to put inside your Faraday cage

What is an EMP?

An electromagnetic pulse or EMP, is an abrupt burst of electromagnetic radiation. EMP energy can be very powerful. Let’s explain that a little better.

To start with, an EMP is caused by certain types of high energy explosions.  An explosion from nuclear weapons, for example, will surely cause an EMP. Likewise, an EMP can be the result of a suddenly fluctuating magnetic field.  Or, as I have mentioned before, it can be the result of Coronal Mass Ejection (CME) from solar activity. But perhaps most sobering of all, is the possibility of a man-made EMP weapon that is purposely deployed in order to wreak devastation on our planet.  Scary stuff.

Regardless of the trigger, an EMP can be devastating to the power grid, resulting in rapidly changing electrical fields that will create fluctuating electrical currents and wild voltage surges.  Bottom line? The electronic gizmos we have come to rely on would be toast. The microchips would be fried or so severely damaged that they would become useless.

So what would life be like following a massive EMP event or episode?  There would be no power, no transportation systems, no communication systems, no banking, no internet, and, no surprise, no food and no water delivery systems.  This would truly be an End of The World As We Know it situation.

Ask yourself these questions:

What if the power went out and never came back on?  Could you fend for yourself?

Could you keep yourself warm in the winter and cool in the summer?

Where would you find food?

What would you use for money if credit cards and ATM’s no longer worked?

How would you get from one place to another without transportation?

How would you wash your clothes?

How would you keep yourself healthy if sanitation systems were no longer functional and medicine could no longer be manufactured.

And the biggest question of all, how would you communicate with the rest of the world?

An electromagnetic pulse could potentially fry the vast majority of all the microchips in the United States. In an instant, nearly all of our electronic devices would be rendered useless.

Back in 2004 the Wall Street Journal wrote:

No American would necessarily die in the initial attack, but what comes next is potentially catastrophic. The pulse would wipe out most electronics and telecommunications, including the power grid. Millions could die for want of modern medical care or even of starvation since farmers wouldn’t be able to harvest crops and distributors wouldn’t be able to get food to supermarkets. Commissioner Lowell Wood calls EMP attack a “giant continental time machine” that would move us back more than a century in technology to the late 1800s.”

With that introduction, today I would like to introduce you to the Faraday cage, and further, how to build a simple Faraday cage.

The Faraday Cage

In the simplest of terms, a Faraday cage is any shielded enclosure that surrounds your electronic devices and protects them from an EMP blast. 

You may have heard Faraday cages referred to as an EMP box or EMP proof box.

Commonly used enclosures include galvanized metal garbage cans, popcorn tins, and even tightly sealed metal filing cabinets. In all cases, the metal container is lined with insulating material to prevent the contents from having contact with the metal.  Examples of insulating material are cardboard, Styrofoam, and even carpet scraps.

More elaborate structures can be custom built from sheet metal but for the home user, why bother?  As a matter of fact, I suspect that wrapping your devices in plain, ordinary, aluminum foil will work as well.

Factoid: Faraday cages are named after English scientist Michael Faraday, who invented them in 1836.

How Do They Work?

Effective Faraday cages protect what is inside of them from static electric fields. This could be an electron or proton as it is a force field surrounding a charged particle. As your probably already know, electromagnetic radiation is all around us, but it is also what Faraday cages are trying to keep out. Electromagnetic radiation is in microwaves, radio waves, ultraviolet light, and visible light, but when it is in these forms it is not harmful. However, when it is stronger, it can be disruptive and harmful to many electronics, and this is when we need Faraday cages. 

When an outside object with an electrical charge gets near the outside of the cage (the conductor, ex: aluminum mesh), the positive and negative particles separate. The electrons that have the opposite charge of the approaching object are drawn to it, and at the same time, the electrons with the same charge are repelled and move away from the external object. This process is called electrostatic induction.

Virtually any type of metal will work as a conductor to build your Faraday cage with. It is usually alright if the cage has small holes in it, as long as they are not too large in comparison to the wavelength of the incoming electromagnetic wave. You can also use an existing metal box to serve as your Faraday cage as long as there aren’t too many large gaps that would allow leakage, so creating a Faraday cage could cost you no money and minimal effort!

What About Using a Microwave Oven?

In my research, I read that a microwave oven, new or used,  can be used as an effective Faraday cage. On the surface, that seems logical since, by design, a microwave oven keeps the energy it creates confined to the interior which likewise, should prevent strong electrical pulses from getting back inside.

This was easy enough to test. I put a cell phone inside my microwave oven and tried calling it. It rang. Oops.  On the other hand, I wrapped my cell phone in aluminum foil and called it. Nothing. Nada. No Michael Buble ringtone; the call went straight to voicemail.

Protecting Small Electronics from an EMP - Backdoor Survival

A foil-wrapped cell phone blocked the cell signal

Granted, cell phones operate at various radio frequencies so while one cell phone may not work, another one will.  Still, with this being so easy to test, why chance it?

Testing the Faraday Cage

Aside from calling a cell phone, you can test your homemade Faraday cage by putting a portable radio inside the shield after tuning it to a strong FM station.  If you can hear the FM station while the radio is inside your Faraday cage, then you need to go back to square one to ensure your shield is properly sealed.

Sealing your garbage can with duct tape will help tremendously.

A Second (Expert) Opinion

I asked my friend George Ure to comment and to offer his perspective on Faraday cages since EMP preparedness is something he covered in-depth on his subscriber site, Peoplenomics ($40 a year but worth it for the technical information on the many topics he covers.).

He was quick to point out several things about EMPs.  The definitive public information is contained In the 2004 Congressional Research Service (CRS) issued a report “High Altitude Electromagnetic Pulse (HEMP) and High Power Microwave (HPM) Devices: Threat Assessments”.  The following diagram shows how an EMP causes the complex systems we rely on to provide everyday essentials for living, to fail in a cascading manner.

EMP Cascade Effect

So, a quick inspection of the EMP failure modes, George offers, is one way to build a list of items to put in your Faraday cage.

He also told me some personal research he’s done that seems to indicate that about 90% of cars will continue to operate after an EMP event of moderate size. The problem, he points out, is that with an EMP, the grid is likely to fail, and with that, power transformers will likely fail, along with the supervisory control and data acquisition systems (SCADA) control systems for railroads, power, water, and other utility distribution.

George’s personal Faraday cage is a 33 gallon garbage can.  He considers his metal garbage effective by itself because the metal lid overlaps the can itself by an inch and radio waves don’t like to go around corners, too well. Still, the ultimate prepping device would be a metal garbage can which has the top cover sealed to the bottom of the can with aluminized duct tape such as the type found at Lowes, Home Depot and other hardware stores.

What to Put in the Faraday Cage

The equipment you store in a Faraday cage should encompass those devices that will help you communicate with the world following a devastating loss of the grid. Short-range communications will be critical after an EMP event. A good starting list would include:

Multiple GMRS radios and chargers along with cables to plug in for solar charging.

Multiple 2 meter and 440 MHz ham radios (such as the portable Baofengs), again with charging cables and solar power adapters.

A laptop computer with a fresh battery, a charger, solar adapter, and all the key software on CD so if you need to bring up a fresh copy of the operating system, you’ll have the product key and then any prepping articles or references you might need.

An AM/FM/Shortwave/NOAA Weather radio that includes a solar panel charging mechanism.

High-capacity USB thumb drive holding  pertinent financial information including past year tax records, scanned copies of birth certificates, passports, marriage licenses, deeds, vehicle registrations and medical records.

A flashlight or illumination devices to help you see in the dark if the power goes out. Having all of the supplies you will potentially need will make everything much more convenient for you in the event of an EMP attack.

Walkie talkies may also be useful for short distance communications, especially with famuly members. Remember that your cell phone is not something you can rely on during and after an EMP event.

George also recommends simple insulation for your electronics, so that units do not touch each other, He uses low tech insulation: a combination of cardboard and bubble-wrap works well.

Protecting Small Electronics Day to Day

This article would not be complete if I did not mention the availability of small, shielded metalized bags that can be used to provide EMP protection on a daily basis.  I am currently testing this type of bag from Mobilsec and am quite impressed. While my phone is in the bag, it reads “no service”.

If a cell signal cannot be detected, I can only assume that an EMP would also not touch it.  Good to know and certainly an option, especially for a laptop that could be placed inside a properly sized bag when not being used.  Couple the Faraday bag with a solar charging system and if there was an EMP, you would still have a working computer.

One other thing. You may find sources online that say that when a device is turned off, it will not need EMP protection.  I reached out to Joel Ho, the developer of the Mobilesec Bagsand asked him about that.  Here is what he said:

I’m assuming you are referring to the part about devices being off not needing protection – it’s simplified a bit – essentially, devices that are off are extremely difficult to damage because there’s no existing current to piggyback on.

Imagine that an EMP is a tidal wave.  If it approaches a full reservoir (electricity and current) it can keep going. If the reservoir is empty (no juice), the tidal wave loses energy navigating the reservoir.

There are hints of this in the article Electromagnetic Pulse Protection by Jerry Emanuelson.

The major reason [most sources] don’t say “your devices are safe if off” is because most devices are usually still connected to power lines and thus susceptible – but if devices are in EMP bags (which by definition are almost always disconnected as the filters are expensive), AND the devices are off, it is unlikely, given the relatively high FCC shielding regulations to prevent excess energy from bleeding OUT into the environment, that enough can get IN to damage those electronics.

This is NOT true for every device – more like a guideline than a hard 100% rule.  Different devices have different levels of built-in shielding – a computer has much more than a $10 Radio Shack timer, for example.

Protecting your credit cards is also something that you can easily take precautions with. There are wallets that are made with RFID-shielding technology (like these). This may seem like something small, but having one less item to worry about in the case of an EMP attack, can save you a ton of stress.

Vehicle Faraday Cage

Keeping a Faraday Cage in your vehicle with you at all times is a necessity because if your vehicle gets disabled by a massive EMP or solar flare, you’ll want to be able to communicate with others in the event that you get stranded.

All you will need in your vehicle Faraday Cage is a spare radio and a spare cell-phone. Having multiple communication devices is a good idea in case one of them has been disabled by the EMP. This can be kept in your glove box or under your seat.

Faraday Cage Myths

  1. Chicken Wire Works Well – Chicken wire provides very little protection from EMP in comparison to foil and metal boxes.
  2. Faraday Cages Must Be Grounded
  3. All Electrical Devices Will be Taken  Out by an EMP Blast – Different nuclear/solar EMp blasts have different frequencies so they won’t all affect the same devices or be able to affect some devices.
  4. All Modern Vehicles Will Not Work After an Attack

The Final Word

Should a massive EMP occur, stores won’t be open, credit cards won’t work, and the gas you have in your car may be all the gas you’ll ever have for months, or even possibly years. When you think about it, an EMP will become the “Ebola virus of electronics”.

That said, you know that I am not a doom and gloomer.  Quite the contrary. I am an optimist to the nth degree.  Yet even the optimist is sobered at the ramifications of an EMP and especially at the prospect of a weapon-based EMP. If nothing else, I would like to have a mode of communication following a massive EMP.

Will the DIY Faraday cage work?  It is speculation to say for sure.  My own research plus my limited understanding of electronics tells me it will, but this premise will remain unproven until an actual EMP event occurs.

The bottom line is that I hope a catastrophic EMP never happens.  But if it does, I want to be ready to fend for myself without electronics. Sure, having communication gear and other electronic gizmos in a working Faraday cage will be a wonderful thing.  But even if it doesn’t work, the goal of preparedness is to prevail, even if that means living in an off-grid society for weeks, months, or even years.

I would like to acknowledge my pal George Ure for his assistance with this article.  His research and first hand experience with Faraday cages, along with his perspective, is appreciated.

Update:  Clearly, there are many unanswered questions and that is to be expected. Rather than answer them individually, I will compile the questions and seek answers from individuals whose technical experience and background far exceeds mine.  Please leave your questions in the comments area below.

Enjoy your next adventure through common sense and thoughtful preparation!
Gaye

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Bargain Bin:  Below you will find links to the items related to today’s article.

Behrens 10-Gallon Locking Lid Can: This 10 gallon can would make a perfect Faraday cage from small electronics.  The locking lid is a bonus although I would still seal the edges with 2” duct tape. This price, by the way, is less than my local Ace Hardware store.  Also available in this larger size 20 Gallon size.

3M Duct Tape: A good quality duct tape is an absolute necessity when sealing your DIY Faraday cage.  For slightly less, you can purchase 3M Utility Grade Duct Tape

Midland 36-Mile 50-Channel FRS/GMRS Two-Way Radios: These are the handheld radios that I own. There are lots of good uses for the these radios. Handy while hiking, traveling, or simply keeping in touch with your partner while out shopping. Just be aware that getting a 36 mile range out of any handheld FRS radio is a myth.

Pofung/Baofeng UV-5R Ham Two Way Radio: Redundancy is the name of the game.  I also have two of these inexpensive HAM radios.  Keep in mind that if you are just planning to listen, you do not need a license (I am still working on mine).  The price is right.  Also consider the NAGOYA Antenna for BAOFENG UV-5R  and the USB Programming Cable for Baofeng UV-5R UV-3R+. Note: the Pofung was formerly known as the Baofeng UV-5R).

SunJack Portable Solar Charger:  SunJack® helps mobile users stay charged on the go anywhere the sun shines. The SunJack® is able to fully charge its internal battery pack in about 5 hours of direct sunlight, or directly power any USB device. When the sun isn’t shining, users can still energize their devices from the powerful SunJack® battery, which holds enough charge to power up to 4 iPhones.

Kaito Voyager Trek Solar/Crank AM/FM/SW NOAA Weather Radio with 5-LED Flashlight: This simple to operate radio can be powered by three AAA batteries or the built-in rechargeable Ni-MH battery which in turn can be charged by hand cranking, by solar panel or even by a PC. . The 7-weather channels are pre-programmed and numbered from 1-7, you can easily and conveniently tune into the stations by adjusting the switch.  Note that not all emergency radios include the NOAA weather band so this is an important feature.

Cell Phone Faraday Cage Bag:  This is the bag I have been testing.  It is also stops hacking and the tracking of your phone.  Mobilsec also has a laptop sized Faraday Cage EMP Shield

Help support Backdoor Survival. Purchases earn a small commission and for that I thank you!

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109 Responses to “How to Build a Simple Faraday Cage for EMP Survival”

  1. Thank you for this well written and informative information. I have been wanting to build a faraday cage for a long this is a big help. I am also building a solar back up using this design https://mmini.me/Solar has anyone ever tried this design?

  2. Never has your column generated as much interest as this one. I find most of the concerns about saving electronic devices a little humorous, since I didn’t have a television, microwave, computer, or cell phone until well into my 30s or 40s. I well remember living without any electronics, and don’t think I would miss them all that much. Water, food, heat, cooking fuel, and light sources, concern me far more than whether I can access my Kindle ebooks and cell phone. Don’t get me wrong, I DO have a faraday cage that holds several electronic devices that might be nice to have in a long term emergency or crisis, but not really counting on them surviving and EMP or CMP.

    • With a small solar charger, some rechargeable batteries and an electric lantern or flashlight, I can have light for years post event in a small bag. To have a year’s worth of candles or lamp oil would take much more room and weight – important if I have to bug out. Same thing with books. Any critical books I have in printed versions, but I have a Kindle with over 2000 books on it that is lighter than one hardcover book…with the same solar charger I can keep it running for a few years post event at least, maybe longer.
      One item that I’m not sure has been mentioned is radiation measuring gear (geiger counters and dosimeters.) I have a bunch of them stored in two faraday cages since an EMP event would likely cause problems for any nuclear power plants even if it wasn’t the opening salvo of a nuclear strike on US soil. It’s pretty hard to know if you’re being exposed to radiation without electronic detection gear, at least until it’s much too late to do anything about it….
      So, sure the electric light and Kindle are luxury items and not strictly necessary, but I consider a geiger counter and dosimeter (or three) a very important prep.

  3. Gaye, You are doing a great job.

    I am a little sceptical regarding some of the solutions proffered; one specific issue is the use of silver foil.

    Whilst silver foil has the ability to protect against an E (electric field) it will not necessary protect against an M (magnetic field). For every E field there is an associated orthogonal M field. One needs to consider the thickness of the protecting material to mitigate M field damage.

    Regards,
    Steve

  4. having trained in electronics in the Navy I begin building my faraday cage from electronic theory. first is that the EMT which is a form of electricity will follow the rules determined by years of research. the electron like the photon tends to follow a straight line when in the free air only air molecules providing the path. second power will follow the path of least resistance. if given a path it will follow it to ground. the faraday cage is nothing more than providing this path. the ideal condition provides the lesser resistance thus providing protection. copper and aluminum providing the best. a gap or opening will let in a signal. using the first rule we see that it will be reflected and with the amount of power in the EMT a reflected signal is as bad as a direct. The goal is to attenuate and weaken the signal. this is where I have an idea that may provide the attenuation and redirection of the EMP. I have tried using some iron powder. the powder I had was quite consistent and did work with the limited power signal I had. my abilities to test are limited so I put this idea out so others with better labs can try it. I also think that using particles of a multitude of sizes would provide more protection. I would embed these particles in a carbon paste that wires are embedded to provide the final path to ground. the design of the container is designed with a cover that requires a signal to reflect twice. the areas providing the reflection surface would also provide the most absorption and path to ground. this providing the best attenuation of signals. the boxes I have built with my poor skills seem to work well enough. what I would like is someone with equipment that is sensitive. to provide testing to prove it works. the idea is to provide a media like a moldable composite of carbon and iron particles. these form the main storage box. the cover providing the blocking path that attenuates all signals. because I am old and time left is short I want to pass on my ideas for others to prove in hops I will have provided answers and protection that is affordable and will work. if it doesn’t? well, I tried. all I want is to provide a safer world for my grandkids.
    Grampa

  5. A lot of great info on EMP and survival .Footnote when i was 4 yrs old 1948, we lived in a log home my father built in western Virginia after he returned from WW2 . It had no heat except a wood burning cook stove No electricity No running water(it came by bucket from a spring )we had a out house for a toilet and a Sears catalog for toilet paper,or frig was a ice box with blocks of ice to hold Butter and other small perishables. We had a huge garden and my Mother canned about 90% of our crop.
    Lets move up 73 yrs. Suverability is something that you could achieve with a small amount of planning
    I have at my home in Fl. a solar still easy to build out of plywood and a piece of glass,I have a 6000 watt off grid Inverter charger, powered by 12 agm 105 amp hr 12 volt wired for 24 volt batteries. To charge them I have One 6000 watt gen and a small 2000 watt for my camper.The inv. is wired to a sub panel to feed my main. It allows me to run the frig and freezer and Irrigation well pump for a water source.Since in a Majuro event Fuel will be non existent in short order,I have 4 220 watt solar panels mounted on a cart to position for max sun gain.
    Lets return EMP prep inthe event of an attack from a foreign power, Hopefully NORAD would be able to give us about 15 min Waring of incoming < the weather channel could give us days of impending Solar flares or the Ham URALL keps track of this also. So a lot of time to move sensitive equip into Protective cages. That only leave saboteurs against our grid , which could also interrupt water supply as well as communication. I think this is the greater threat after social discord.Plan for the worst hope for the best .( buy C rats )
    As a bragging foot note I lived in Homestead Fl.The house I had built there survived Hurricane Andrew with only wet carpets, My Family of 6 lived on gen Power for 31 days. We were one of the first to have power restored some went 4 or more months, as you know parts of Porto Rico are still without power 8 months after a simple Hurricane.

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