Tired of your cellphone always being connected doing who knows what in the background whether you want it to be or not? With this simple signal blocking box you can block most phone signals when you don’t want them and allow them when you do. Perfect for storing in your car trunk it will both block signals and protect your phone from damage while traveling.

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Here is a complete list of Supplies & Tools you will need. They are not all the same supplies I used but should be similar or better replacements.

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Supplies

• Outdoor Watertight Case – (The main box for the project to be made in. This project will effect the waterproofing seal so I would not use it in highly wet conditions.)
• Copper Foil Tape with Conductive Adhesive – (The adhesive side must be conductive or the signal will escape through the overlaps.)
• Foam Packing Sheets – (I used ones I had lying that came in a box of something I ordered. These are the same type of foam in 1’x1’ sheets and 2 in thick in a 2 pack.)
• Your Cellphone – (You should already have this for the project but if not here is a link to some cell phones.)

Tools

• Scissors – (Used for cutting the copper foil tape.)
• Box Cutter Craft Utility Knife – (I used a small retractable blade but these utility knives would work much smoother.)

Measure the copper tape by laying it down on the bottom and then cut a strip. Then hold the strip up to the tape and cut 2 or 3 additional ones the same length.

Peel the adhesive backing paper off one end slightly then place it in the bottom and press down to stick it while slowly peeling more of the backing off. This way it sticks better and won’t get covered in the oils of your skin which may cause it not to stick as well. Be sure to make each strip overlap the last strip. This tape is conductive on both the front and back adhesive side so it makes great contact when overlapped which is important for signal blocking. Fill any gaps and holes that happen with more tape so there is nowhere for the signal to escape. The tape is very thin so if it rips just cut another piece and put it over the damaged part.

Apply it to the side wall from the top down overhanging onto the case edge slightly down to the bottom. Do one small piece at a time while pulling of the adhesive backing again. Don’t worry here if there is a gap its bound to happen between the side and the bottom we will fix that in the next step.

Don’t worry if you end up with a large gap like I did, just take a strip of tape and cut it in half down the center and apply it overlapping the two sides and the gap.

Now cut a piece of the copper tape and then cut it half again and then apply these strips into the corners trying to get it as flush as you can. My box has plastic groves for some rubber thing that came with it that I removed as it wasn’t needed for this project, so I had to place a few layers over its corners leaving a slight air gap. If your box has groves on the corner its easy to tear the tape pushing on the corners so be careful and its okay if there is a air gap on the back as long as the tape has no holes or rips. The important part is that the copper layer itself has no damages and acts like one solid conductive piece.

Apply tape to the other sides like the prior steps. Be sure to get the tape into those corners the best you can even if it takes a few layers. If your box has even larger corner ridges that the foil cannot cover without ripping you can put down a layer of something like packing tape first to create a cover and then put the copper over it or use a rotary tool to remove the ridges on the corners.

Now we need to apply copper tape to the edges of the lid so that when the two sides meet it makes excellent contact between the lid and bottom. Note this will make it no longer water tight but is required to achieve the best signal blocking. If you have to have it be water tight get another box that is bigger that can hold this box and place this box in that one. I took a strip of tape and then cut it half, then I cut those two halves in half again giving me 4 thin strips to work with. It took more then this to go all around the ridge so cut more as needed. Be sure no gaps or holes are on the edges.

Time to repeat the same thing on the box bottom like you did on the lid or vice versa if you started there first. Its easiest to do the bottom first then the side walls and fill in the gaps. I did 4 strips which worked a bit better then the 3 I did on the lid.

Cut some more strips into fourths and apply it all around the edges again where the lid and box bottom make contact. These pictures show the before and after. I did have some parts already that overlapped it so those I just put a little more starting from there and went around the rest. I found the curved corners to be easier by cutting one strip into thirds then applying them. It is fine if it overhangs the outside. Be sure it makes good contact with the inside of the box with no gaps.

I did a quick signal blocking test just by setting my phone in the box. For better results don’t have your phone make direct contact with the copper tape like it did in this example. The blocking works best when the copper tape and phone have a non conductive layer between them. It did show signal blocking still on this test and I didn’t see any gaps, rips, or holes so I continued.

This both stops the phone from making contact with the tape directly and provides protection to both the tape and your cell phone so if you store it somewhere like your car trunk your phone will be protected from damage that it could potentially get by shaking around inside the box without anything. The phone bouncing around could also tear and rip the copper tape all over inside the box so foam sheets like I had, styrofoam, cloth, or anything else that can hold it snugly in place is highly recommended. I used some scrap foam sheets I happened to already have lying around that came in the box of some item I purchased. This is the step where having the utility craft knife will be most helpful, scissors can kind of work but a sharp blade works better. It doesn’t have to be a perfect fit just enough that the phone won’t rattle around too much inside it.

I also cut a cover to go over my phone to protect the screen further. If your foam is large enough you could also fit multiple cellphones and just cut a foam sheet to go between each phone to protect them all from damage. I used a bubble mailer envelope as a straight edge, a ruler would work better but it doesn’t have to be perfect it just made the cut a bit cleaner.

If you bought the foam sheets you will not have to do this step but since I used scraps I had to also fill in the gaps. With the main foam box with a foam lid holding the phone done now all it needs is some strips to keep it centered in place. This helped but the phone can still escape the foam box with the gap between it and the lid, so the next step is required.

I cut a large sheet for the lid but it still needed a little bit more to make it snug in place so I took two strips of foam and taped them together then pressed them on top of the lid and it stayed in place with just the pressure of the foam against the side walls. This puts just enough pressure to keep the foam cover over the phone. Don’t have it put too much pressure on the phone screen or it could potentially cause damage like cracks as phone screens are very fragile and it doesn’t take a whole lot to break them from too much pressure on the screen. This puts just enough pressure to keep the foam lid in place and prevent the phone from rattling around or moving at all while also being just loose enough not to cause the screen any damage.

With the foam in place the signal blocking box is now completed. It will both block the cell signal and protect the phone while traveling. Now you can just place your phone inside when you want it to not be able to connect and remove it when you want to use it.

I ran a few tests to see how well the signals got blocked using a few apps: one of which is MD Faraday Bag Tester for testing Cell Signal & Wi-Fi Signal Tests, the other app I used is called GPS Test for testing GPS signals. The box successfully blocks all the cell signals and GPS signals however Wi-Fi did manage to still get through. Though the location I tested it was one room away from the Wi-Fi router which is part of why it didn’t block it fully. Even with Wi-Fi getting through it blocked the two I most wanted blocked. To fully block Wi-Fi will likely require a second smaller box inside this one also covered in copper tape inside just like this one. If you try to do multiple layers in a single box you can’t have the previous copper layer touch the new layer or it will just act as one layer since it is conductive. You could also try thicker layers but that wont help nearly as much as another box that is also signal blocked or separate isolated layers. Since the outer box used is the main protective box for any additional nested boxes you could use cardboard boxes covered in the copper tape though cardboard inner layers will not last quite as long as the hard plastic will with constant use.

Here are some upgrade ideas:

• Get a smaller box that fits inside and copper tape it like this one on the inside so they are two isolated signal blocking boxes nested in each other would provide even stronger signal blocking. You could even use something like cardboard for the inner layer since the outer layer is hard plastic and will protect most things inside though cardboard will not last as long with constant use.
• It would be harder to do successfully but you could try to isolate a second layer with packing tape or some other non-conductive tape and then place another copper layer over it. The hard part would be the edges because the separate layers cant touch each other but for best signal blocking the individual layers have to meet on the edges for less signal leak potential.
• Placing your phone in a homemade or purchased faraday bag inside of this box would also block more signals. You can put your phone in a plastic bag wrapped in tin foil and then another plastic bag so it won’t accidentally make contact with the copper to get more signal blocking. However tin foil does not last very long and after about 5 times of removing your phone the layer will have rips and holes.
• You could implement a small phone charger inside of this such as this one to be able to charge your phone while its being signal blocked, just don’t let any of the metal parts of the charger power bank touch the copper layer or it will short out the battery and could explode. If you want it to have a charger having it inside a plastic non conductive box with the phone placed inside of the signal blocking box is probably a better idea. Also keep in mind the heat generated from charging from the power bank and your cell phone will be trapped inside with nowhere to go so be sure it doesn’t get so hot that it can ignite the foam layer or it will become a fire hazard. I would also avoid fast charging power banks as they produce a lot more heat rapidly.

If you would like to support me in making these projects you can do so here.

Do you have any more suggestions? I will add good ones to this list and if there is enough demand I will possibly do some of these ideas in the future.