Faraday Pockets




Introduction: Faraday Pockets

About: I'm Mike and I make crazy things at Instructables HQ in San Francisco. Follow me and try a few of my projects for yourself!

Hide your cell phone by blocking any incoming or outgoing radio frequencies with a Faraday pocket. Whether you're looking for an easy way to immediately silence your phone when at a movie theater or stop those annoying incoming calls from your crazy ex-lover, Faraday pockets have you covered.

By lining your pocket with a special fine mesh metallic fabric you can reflect incoming fields and absorb energy. The effect of protecting something with a conductive fabric is called a Faraday cage and is named after Michael Faraday, whom first discovered the phenomena.

Making your own is easy, and a fun way to experiment with a neat scientific property of electrical field cancellation.

Ready to make the best pants ever? Let's make!

Step 1:

You'll need a pair of pants which you are willing to modify. Luckily the modification is just to the pocket, and even then isn't much of a modification, so you won't be ruining your clothes with this project.

Along with scissors, a fabric marker, and a sewing machine you'll also need conductive fabric, I used nickel/copper rip-stop as it has a high shielding rating and is easy to work with. There's loads of other options available, so experiment and have fun!

Luckily, the shield layer of conductive fabric doesn't have to be very thick:

The conductive layer can be very thin because of something known as the skin effect. That term describes the tendency of current to flow primarily on the skin of a conductor. As long as the conducting layer is greater than the skin depth, it will provide excellent shielding because the absorption loss will be large. The skin depth is a function of the frequency of the wave and the conductor material. As an example, consider that for a frequency of 200 MHz, the skin depth of aluminum is only about 21 microns. EMP pulses can have frequency content that ranges up to 1,000 MHz. Therefore, wrapping a box in a couple of layers of heavy duty aluminum foil (typically about 24 microns thick) provides the necessary conductor thickness to protect against high-frequency radiated fields. (source)

Step 2: Outline of Pocket

Turn pants inside out and place a corner of the conductive fabric under the pocket flap making sure that you're getting the corner of the conductive fabric all the way up into the underside of the pocket as far as it will go.

Using your fabric marker trace the outline of the pants pocket on the conductive fabric.

Step 3: Cut

Remove the conductive fabric from under the pocket flap and cut along the traced outline, then use the cutout as a pattern to cut a corresponding piece for the other side of the pocket.

Cut a generous outline outside the traced outline for you to sew into, you can always trim it down later.

Step 4: Pin

Place the cut sections of conductive fabric on either side of the pockets on your inside out pants.

Pins were used to located the conductive fabric where I wanted. It's important to cover as much of the pocket as possible - completely is possible.

Step 5: Sew

I used a sewing machine with regular thread to do the majority of the sewing. Each conductive pocket side was sewn together onto the existing pants pocket, the more difficult sections to sew were finished by hand with a needle and thread.

Step 6:

Check to make sure the pocket edges are sealed, and that as much of the pocket is covered as possible.

Can it have holes or openings?

Yes, as long as the holes are small with respect to the wavelength of the incident electromagnetic wave. For example, a 1 GHz wave has a wavelength of 0.3 meters in free space. As long as the holes are significantly smaller than that dimension (i.e., a few millimeters), they won’t let in much of the incident wave. This is why fine conductive mesh can be used when constructing a Faraday cage. In practice, the cage’s lid or door usually causes the most leakage. Taping the seam with conductive tape helps to reduce this leakage. (source)

Step 7:

With your pocket modified you're ready to turn your pants right side out and test out your Faraday pocket.

For best results, your phone should sit entirely inside the conductive fabric lined pocket. Any opening will allow signal to be transmitted to or from the device and nullify the Faraday cage effect.

Have you made your own Faraday cage?I want to see it!

Share your version in the comments below, comments with a picture will get a free Pro Membership to Instructables!



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83 Discussions

Perhaps clothing makers should make this standard in all teenager's pockets. lol

Someone commented and said this was to protect against an EMP event. Hmm...with the device in my "faraday cage pocket", I can not make or receive a call. But after the EMP event I have a good phone that works. Ah...all towers will be non-functioning. So what good is the phone? Can't use it in my pocket, and can't use it after the EMP event. Who would I call if the towers were still up?

Like I said it might be good to store car keys and credit cards, but it's useless for a cell phone. Poorly thought out. I think maybe the aluminum foil interupted the brain waves.

2 replies

I am no survivalist, but simply put forth a hypothetical situation. well i guess EMP attack can be localized (more so in war zone)... then, your phone can operate once you make your way to an other region. Also GPS works with Satellites, so i if they aint broken, you can get a rough idea of location even if there is no cellular network, right? Of course more poetic people can shoot video tapes of their survival journey right?

hi, larry. i thought, @ first, that THAT's what it was for ~ plastic card protection. ☺ it does that as well?

nice, will this work to protect my credit cards in my wallet in my pocket?

1 reply

The apocalypse would be a lot more boring without your angry birds. I jest. I believe this to be more about privacy, and protecting oneself from big brother.

Although, if there were an EMP burst, there's more functions on a smartphone that would be useful other than cellular calls in such an event. There's GPS (provided the satellites are not toasted too), stored files such as scientific, and medical data, books, music, etc.

Personally, I'd rather wrap my phone in foil, or store it in a metal box. I'm not into sewing enough to altar all my jeans, and if you wear fatigues, or cargo pants and keep your phone in your leg pockets, this is not a useful hack.

Wouldn't it be easier to just sew a little phone pouch with a flap that you can stick your phone into any pocket with?

1 reply

That was my thinking too: either a detachable pocket that could be attached to your trousers without impairing its function (that you can remove before washing so as to not wear the fabric out) or a kind of sleeve that would protect the phone regardless of it being in a pocket or not. More keen on the former though; I feel like the sleeve would not be quite as secure...

You can wash conductive fabric, but repeated washing will reduce the fabric durability and reduce the effectiveness of the conductivity.

You know that mobile phones regulate their transmission power depending on the strength of the received signal? If there is little or no reception, the base station must be far away, so send with full power and search, search, search until the base station is found. So expect empty batteries and hot (well warm) pockets.

There is a solution for your problem: flight mode.

5 replies

awww. That's just not as fun though. Faraday cages are so much cooler

...except when your workplace unintentially wraps your whole building in one. My building is wrapped in a mesh to keep the building cooler (it really does work!). However it also works as a partial Faraday cage. Mobile phone reception is terrible!

To keep it cooler, or to protect file systems from hackers outside the building?

No it was to keep the building cooler. There are too many gaps and no mesh on the roof or basement. Annoyingly, for architectural balance, they decided to put the mesh on the side that does not get any sun (south side of the building as I am in the southern hemisphere). It is super annoying to look through. It messes with your eyes. Also as it is sprung to be flexible in the wind it also sounds like you are on a boat on windy days. Lol. But I'm sure they are saving a motza in air conditioning bills.

Damn! It's a good idea for cooling, if not for modern times. You should have your IT department set up a repeater system or something hah.

The power ramps up with a poor or missing signal?
Yikes! Remind me to never put one in my front pants pockets!

This will stop incoming and outgoing radio frequencies. Not just for EMP protection or annoying ex protection, it's also for those people who like to think their nuts are frying from WiFi. The same people you see wearing aluminum foil on their head.

This is awesome! Just be aware that doing this may cause your battery to die sooner, due to the fact that it will be constantly searching for networks to connect to. On the plus side, it will be safe from those pesky, electronics-frying EMPs.

2 replies

Yes, by all means we should protect our electronics from EMPs... but what about ourselves? The devices that make EMPs also make a big shockwave, flash, heat, radiation, even fallout. Any thoughts on how to shield our bodies from those things? :)

If only there was a fabric we could use to make faraday clothing we could be safe!!