Estimated reading time: 23 minutes
They’re Easy to Build and Protect More Than You Think.
A Faraday cage is a simple construction of an insulated box or container surrounded by metal to protect electronics from various forms of electromagnetic transmissions.
The worst-case scenario is an EMP or electromagnetic pulse released by a nuclear detonation or an event occurring naturally from outer space like a solar flare. A more common scenario is the growing threat engineered by hackers attempting to access electromagnetic transmissions through cell phones, RFID chips, and electronic car fobs.
In all instances, many electronic devices can be at risk from computers to flashlights. Most people are either unaware of the risk or dismiss it as too extreme. The unfortunate fact is that more and more unwanted and illegal attempts to access electronics are occurring and some Faraday cage products have shown up on the market to protect basic electronics from hackers on a day-to-day basis.
Michael Faraday was a 19th-century British scientist who established the basis for the concept of the electromagnetic field in physics. In 1836 he invented a cage surrounded by wire mesh which effectively prevented electricity or electromagnetic fields from penetrating the interior of the cage.
The invention was a bit of a novelty but over time has emerged as a standard design to protect both people and electronics from any damages caused by all things electric. Here are some “current” examples:
- Linemen working on electric power lines wear metallic Faraday suits designed to protect them from deadly electric shock.
- Police use Faraday cages to protect confiscated cell phones from being remotely compromised or altered after they are seized.
- Entire MRI scanning rooms are designed as Faraday cages to keep unwanted electromagnetic radiation from interfering with MRI scans.
- Government and military installations are also surrounded by metallic walls to shield sensitive electronic equipment. In fact, NORAD just relocated back to Cheyenne Mountain to take advantage of the natural Faraday shielding of the mountain.
- Switzerland passed a law that all sensitive electronics related to the power grid must be shielded by a Faraday cage.
- The same legislation was recently passed in the state of Maine.
- Intelligence services use Faraday cages to protect and effectively cut off radio waves to protect confidential information, and Faraday installations are used extensively by intelligence services worldwide.
So Why Do I Need A Faraday Cage?
Maybe you don’t. A lot depends on your general level of concern about things and the degree to which you use and depend on electronic devices. The EMP threat to electronic devices is the widespread destruction of the electronics in any piece of equipment.
If a computer or anything else that depended on electronics to function was hit with a burst of electromagnetic radiation, the circuitry is fried and the electronics cease to operate. Some reports indicate this could cause a catastrophic failure of the power grid. Or not.
While the effects of an EMP burst from a nuclear detonation would spread for hundreds of miles and could have devastating consequences, the everyday threat that has emerged is coming from hacking and privacy invasions.
It might make sense to store some spare electronics in a dedicated Faraday cage in the event of a catastrophic event like a nuclear detonation or even a random EMP burst from outer space. It’s also worth thinking about protecting some everyday electronic items that are becoming more and more at risk.
We’ll mention some commercial products that can protect your electronics, but we’ll also cover the do-it-yourself options later.
Electronic Car Keys
Some newer model cars offer an electronic and remote engine starting capability. The promise is that you can start your car from you house in your winter pajamas during breakfast, and have it warmed up and ready to go when you are.
The danger is that car thieves have figured out how to remotely access the electronic signals for those electronic keys even when they’re laying on your nightstand next to your bed. Commercial Faraday protectors for electronic car keys have started to show up and they highlight the growing threat.
Hackers have moved beyond computers to cell phones as a prime target for hacked invasions. Some of the attacks are purely vicious and designed to simply destroy the function and memory on a wireless device.
Others are more targeted in an effort to gain access to personal and financial information. Here again, commercial Faraday cage products are beginning to show up to protect cell phones from hacked intrusions.
Most major credit cards have something installed called an RFID chip. It should come as no surprise that hackers have figured out a way to access those chips while the credit card is residing in someone’s wallet or purse while they’re in line waiting to check out at the grocery store.
Once they have your RFID code, they can use the code just like your credit card. New wallets have started to show up with Faraday shields that protect against RFID hacks, but a dollar-bill-sized piece of aluminum foil in your wallet or purse can help to “foil” the hackers.
Computers have always been the biggest concern when it comes to unwanted electromagnetic radiation from both widespread events like an EMP burst to everyday hacks from individuals and even rogue nations.
And it’s not just the electronics but the wireless capability that is vulnerable and, as you would suspect, commercial products have also started to appear to offer everyday protection to laptops and pad devices.
Here’s a new one. People sometimes discover that their neighbors are “borrowing” their wireless signals from their wireless modems. This doesn’t just affect data speed related to bandwidth—if you have a fixed amount of data on a monthly basis, they’re stealing your data allowance.
The result is you pay more or have compromised bandwidth for downloads and streaming. We’ll cover a way to partially block your wireless modem to prevent theft of your Wi-Fi by a neighbor or even that guy sitting in his car who always parks in front of your house.
As more and more everyday items become wired into wireless networks the threat will grow. It’s enough to make you think twice about wirelessly controlled washing machines, refrigerators, furnaces, and those doorbell video cameras.
Are DIY Faraday Cages Foolproof?
Usually, although a homemade Faraday cage could have some weak points.
One simple test is to put a small, portable radio into your DIY Faraday cage. The standard recommendation is to turn it up loud and select the strongest and clearest radio channel you can find. If you can’t hear anything after it’s sealed in your Faraday cage, that’s a good sign that radio transmissions or any other electromagnetic forces are not getting into the interior.
Another technique is to put a cell phone into the homemade cage and seal it shut. Have someone call it and if it rings, there’s a leak—although there are occasions when at least a weak signal could get through.
The only alternative to these improvised tests is to buy some fairly expensive diagnostic equipment to measure the electromagnetic fields inside the cage. They’re called EMF meters that measure electromagnetic force or “EMF.”
That may be taking things too far and you might as well buy a commercially produced Faraday cage rather than spend all of your money on testing equipment. However, a lot of what we’ll be exploring is designed for a rapid piece of DIY construction in an emergency or someone on a tight budget, so some of us will have to rely on radios and cell phones for testing.
As a general rule, metal surfaces with welded seams or at least seams you seal with aluminum tape usually give you a reasonable amount of assurance that you have built an effective Faraday cage.
The weakest Faraday cages seem to be the ones constructed of wire. They represent the original design of Michael Faraday’s first cage and literally looked like cages, resulting in the name. For that reason, we’re going to skip any designs made with chicken wire or aluminum screening, but on a fundamental level, they work the same.
The Basic Concept
We’re going to be enclosing a space with metal. The size of the space depends on what you’re trying to protect. The metal resources we’ll use are easily available and include:
- Metal garbage cans
- Metal cabinets
- Heavy-duty aluminum foil
- Pressure cookers
- Foil insulation bags
- Metal water coolers
- Commercial Faraday fabric (can replace foil if your budget allows)
All of these items are common, relatively inexpensive, and are natural designs and materials for a Faraday cage. Many will need some additional (but easy) work to ensure they’re sealed tight from any electromagnetic field and properly insulated from the metal sides.
Sheet metal is another option, but working with sheet metal is a little dangerous and a bit complicated for most people, so we’re going to keep it simple.
You also need to insulate the interior. If the electronics come in contact with the metal, the electromagnetic field will be transferred to the piece of equipment. All of these insulating materials cannot and do not conduct electricity.
Once again, some common items can be used for insulation including:
- Foam rubber
- Bubble wrap
Let’s Build Some Faraday Cages
We’re going to look at 11 simple designs for a Faraday cage across a range of sizes. There’s no reason to construct all of them, but if you have some of the materials we identify, this will give you some basic advice on how to put it all together to make a Faraday cage.
- Scissors or shears (Most of what you’ll be doing is cutting foil, tape and various forms of insulation).
- Metallic tape
- Cardboard or other insulation like foam rubber, thick plastic, or pieces of wood cut to fit
1. Cell Phone Faraday Cage
A small bag or pocket of insulated foil is perfect for a quick and easy to reuse pocket Faraday cage. This particular type of shipping foil often wraps smaller food items, combining bubble wrap with foil. You’ll need to add a layer of insulating material to prevent the phone from coming into contact with the foil.
If you have any concerns about someone hacking your cell phone, you can use it either in your car, overnight while it’s charging, or any other time when your phone is idle and not in use. Don’t put it in the pocket if you’re expecting a message or phone call. It won’t work.
Cut a corner pocket of the material that will allow your phone to fit. Make it a little larger because you’re going to need to put some insulation on the inside of the pocket.
Staple or metal tape the open side of the pocket you cut, but make sure you leave a flap to fold over the foil on your phone.
You can use binder clips to keep the pocket closed or a snap. Call it to test.
You could also buy a commercially made cell phone Faraday cage.
2. Foil Wrapped Cardboard Boxes
This is a very simple construction, but the important thing is to ensure you have no open seams around the box or on the lid. Use some tape to hold it together. If you want to use metallic tape, all the better. You’ll need a box and a lid. Shoeboxes and cigar boxes with tight-fitting lids work best.
Don’t put foil into the interior of the box. The cardboard acts as insulation. Depending on the size of the box you can do the cell phone or radio test.
3. Foil Wrapped 5-Gallon Bucket With Lid
It gets a bit fussy when you have to wrap foil around a 5-gallon bucket, but they’re inexpensive and the bucket plastic gives you automatic insulation. Here are a few steps to take:
Bend two layers of foil over the base of the bucket and fold down around the sides.
Remove the handles. Wrap two layers of foil around the outside of the bucket sides and fold down into the bucket about an inch and tape in place.
Wrap the lid with two layers of foil and press to hold in place. Tape if you need it.
You don’t want any foil sneaking down the interior of the bucket. You need the plastic to serve as insulation.
Press the lid on to seal.
4. Metal Garbage Can
This is mostly an insulation project although you might want to seal any seams.
Line the bottom and sides of the interior of the can with cardboard.
Seal any seams or rivets with metallic tape including the handles. Tightly press the lid on top and anything inside is protected.
5. Pressure Cooker
A lot of us only use a pressure cooker once or twice a year for canning and preserving, but it makes a great instant Faraday box. The thick metal walls and lid of a pressure cooker give it excellent Faraday qualities. Insulation is the only thing you have to do.
Insulate the interior of the pressure cooker with cardboard, foam rubber of any other insulating material that won’t transmit electricity.
Place your items inside and seal the lid in place and you’re done.
6. Insulated Metal Water Cooler
This is one of the easiest of the bunch because the interior insulation is already in place and it’s surrounded by metal.
You’ll need to seal any seams like you would do on a garbage can.
Most have a plastic spigot towards the base. Cover it with metallic tape. If you want to be double sure, fold some heavy-duty foil over the area and then apply the metallic tape.
The lid has a metal rim so when you press it down, you should be good to go.
7. Foil Shipping bags
If you’ve ever had fresh or frozen food shipped to you, you’ve probably seen those large insulated bags. They have a metallic coating on the outside and plastic insulation inside. If you want to be double sure, place a bag inside a bag, and roll and seal the top.
Make sure the contents are not in contact with any of the metal coating towards the sealed top.
8. WiFi Protection with a Faraday cage
This could be as simple as putting a double sheet of aluminum foil on the wall behind your modem between your house and your neighbor. The same thing goes for that guy parked in front of your house every day.
If you want added protection, place your modem in a foil-lined cardboard box with the open end towards your computer.
9. Instant Faraday Wallet
If there’s one project you should do, it’s to add a strip of foil to the dollar bill pocket in your wallet. When the wallet is folded and closed the foil effectively blocks anyone from hacking the RFID chip on your credit cards.
It’s easy to make and all you have to do is cut a piece of foil the size of a dollar bill and put it in your wallet. If your wallet is larger, cut it to fit. You could also use a piece of adhesive aluminum foil.
10. Metal Storage Cabinet
Many storage cabinets are metal and if they have good seams all around you should have an effective Faraday cage. To test for seams leaks, put a bright light inside the cabinet in a dark room and shut off the lights.
If you see any light leaking through a hole or seam, seal it with metallic tape on the inside where it won’t be seen. Insulate the shelves with foam rubber, rubberized car mats, or even cardboard. It’s a great way to store multiple items long-term in addition to short-term easy access.
11. Your Car Trunk
It’s not the perfect Faraday cage, but you should know that the trunk of many cars do an effective job at resisting the effects of electromagnetic fields. A lot has to do with its position and the electromagnetic event, but the trunk of your car has many of the characteristics of a Faraday cage and in an emergency could be a good place to quickly store any electronics.
Can You Do Better?
You could. If you have the skills, tools, and materials you can fashion a Faraday cage customized to your needs. You could also make Faraday cages out of other found items like metal mailboxes, metal milk boxes, metal ammunition boxes, even a gun safe.
The important thing is to remember the concept: solid metal sheeting without leaks or open seams with an interior insulating material to keep the contents from coming in contact with the exterior metal.
What Should You Put in a Faraday Cage?
It’s probably best to think long-term and short-term. Long-term items are the things that you would stockpile for a catastrophic emergency. Short-term items are those everyday things we already mentioned.
With that in mind, it might make sense to have a Faraday cage for long-term storage and separate and smaller ones for the everyday things you want to protect. Here again, it depends on your level of concern and the current situation.
This could be as simple as a metal cabinet in the basement or any one of the other designs we covered depending on how much stuff you plan to store. This is also a good argument for customizing and designing your own on a large scale. Just remember to apply the concept to anything you build.
Here are some items for long-term storage:
- A spare solar, hand-cranked radio.
- Old, unused cell phones and chargers.
- An old laptop that’s still functioning but no longer used.
- Walkie-talkies or portable HAM radio equipment you don’t use regularly.
- CB radios you longer use.
- Tactical flashlights and headlamps especially if they are rechargeable.
- Electronic watches you no longer wear or a spare.
- Any other electronics you think you’ll need but don’t need on a daily basis.
These are smaller Faraday shields that you can use if you’re concerned about hacking or other criminal activities. You could keep one in the bedroom and just toss things in when not in use, or have them setup at a dedicated place like a desk where you keep your laptop.
Here are some thoughts for short-term Faraday cage storage:
- Electronic car keys and don’t forget that extra key in the kitchen cabinet.
- Cell phones you actively use.
- Laptop or pad devices with their own Faraday shields.
- A cage around your Wi-Fi Modem.
- Any credit cards or the wallet used to hold them.
If your short-term items are stored in a Faraday cage that is constantly visible on a dresser, cabinet, or shelf, you might want to buy a commercially made Faraday cage. They’re not only effective but they’re relatively compact and look much better cosmetically rather than a shoebox wrapped in tin foil.
One thing to keep in mind is that there are many items we have at home that can quickly function as a Faraday cage. If you have that large, metal cabinet or a metal water cooler and want to play it safe, you should think about some electronic items you might tuck into ready-made Faraday cages.
Do You Really Need one?
The answer is a clear and definite… maybe. If a nuclear detonation occurs, we may have more to think about than the fact that our cell phones won’t work. Then again, a solar flare or EMP burst from space would cause no explosive detonation but the effects on electronics and the grid could be devastating. In fact, an EMP would most likely wipe out the infrastructure for all cell phone transmissions to say nothing of the grid.
It’s more likely that a small-scale, highly targeted attack from a hacker or car thief will present the most immediate threat. It’s not uncommon for people to dismiss concerns like that until it happens to them. That’s up to you. If you’re not concerned or don’t care, you probably haven’t read this far.
On the other hand, people who prepare for things tend to consider possibilities. In that regard, the number of potential threats may be significant enough to at least protect that wallet and car keys. And maybe just to be safe, think about that cell phone too.