Cell Phone Faraday Cage

Here's what you'll need...
  • Soup can
  • Aluminum foil
  • Cell phone
  • 2nd phone (any kind)
  • Heavy book or weight

Cell phones are great… except when they don’t work. Elevators and stairwells are common culprits, and then there are those rooms that just seem to be dead zones. The strongest dead zone is a Faraday Cage -- and you can make one!

First, test to see if the cell phone has a signal when it is surrounded by metal on all but one side: Put the cell phone in the upside-down soup can, with a book or other heavy weight on top to keep things in place. Call the phone. Because cell phones get their signal from a cell phone tower (not from the other phone) it doesn’t matter how near the phones are to each other, or if the calling phone is a cell or land line. Does the cell phone in the soup can ring?

It should. Radio waves travel easily through wood and most other table surfaces. Next, repeat the experiment with aluminum foil under the can. Did the phone ring this time?

Because metals are electrical conductors, their electrons move freely and naturally move toward neutralizing electrical fields around them. Any metal container can become a Faraday cage. For electric fields caused by static electricity, it even can have many holes in it and still work. Cell phone signals, though, are a bit different.

Cell phones get their signal through electromagnetic waves. Part of what is “waving” is the electric field, and this back-and-forth field is not canceled out as easily. So, the cell phone signal gets weaker as it goes through the metal, but isn’t stopped in its tracks.

In most cases, metal even as thin as the aluminum foil is enough to weaken the signal to the point of the phone not working. If the phone still rang, it could be because a cell phone tower is nearby and the signal was extra strong to start with.

If there is a small hole in the Faraday cage, it may still dissipate the signal enough to block it. You can poke holes into the aluminum foil and see how big they can get while still blocking the signal. Then, try it again using a phone from a different carrier. Different cell phone brands use different frequencies for their signals, and this can make a difference, too!