# Jamming Cell Phones **URL:** \ **Category:** Factual Questions\ **Created:** [September 26, 2003, 10:01am UTC](https://boards.straightdope.com/t/jamming-cell-phones/203937 "2003-09-26T10:01:48Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Markxxx](https://avatars.discourse-cdn.com/v4/letter/m/5daacb/32.png) [@Markxxx](https://boards.straightdope.com/u/Markxxx)\ **Post date:** [September 26, 2003, 10:01am UTC](https://boards.straightdope.com/t/jamming-cell-phones/203937/1 "2003-09-26T10:01:48Z")
I reckon this is possible. Now it seems in the health clubs I go to this is become the THING. I have seen two people in the last week fall off treadmills while talking. I crashed into another one not looking where she was going etc. You get the point. Could you make wallpaper out of some material that would cause a cell phone not to work so when you are in say the health club floor it wouldn’t work? ---
**Author:** ![alterego](https://avatars.discourse-cdn.com/v4/letter/a/6bbea6/32.png) [@alterego](https://boards.straightdope.com/u/alterego)\ **Post date:** [September 26, 2003, 11:16am UTC](https://boards.straightdope.com/t/jamming-cell-phones/203937/2 "2003-09-26T11:16:07Z")
I think cast iron would do the trick. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [September 26, 2003, 12:20pm UTC](https://boards.straightdope.com/t/jamming-cell-phones/203937/3 "2003-09-26T12:20:04Z")
You need to make a conductive box out of the building. It doesn’t need to be solid metal. It can be metal with holes in it, as long as the holes aren’t bigger than about half of the wavelength. In other words, a metal screen will work just as well as cast iron, and wouldn’t be anywhere near as heavy. Do a little research on “faraday cage” if you want to know more about the theory behind it. ---
**Author:** ![Cluricaun](https://avatars.discourse-cdn.com/v4/letter/c/bb73d2/32.png) [@Cluricaun](https://boards.straightdope.com/u/Cluricaun)\ **Post date:** [September 26, 2003, 1:56pm UTC](https://boards.straightdope.com/t/jamming-cell-phones/203937/4 "2003-09-26T13:56:51Z")
I normally would never link to advertisements on the sdmb, but this company claims to produce just such a product. [http://www.cell-block-r.com/](http://www.cell-block-r.com/) But here’s the deal, I can’t find the cite right now, but short range jammers in use in public (this came from my idea about the same thing at the movies) is illegal without proper licencing of the device. So, there you go. ---
**Author:** ![Cluricaun](https://avatars.discourse-cdn.com/v4/letter/c/bb73d2/32.png) [@Cluricaun](https://boards.straightdope.com/u/Cluricaun)\ **Post date:** [September 26, 2003, 1:59pm UTC](https://boards.straightdope.com/t/jamming-cell-phones/203937/5 "2003-09-26T13:59:20Z")
Here’s the cite: [http://asia.cnet.com/newstech/communications/0,39001141,20098551,00.htm](http://asia.cnet.com/newstech/communications/0,39001141,20098551,00.htm) ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [September 26, 2003, 5:10pm UTC](https://boards.straightdope.com/t/jamming-cell-phones/203937/6 "2003-09-26T17:10:49Z")
> [@](#): > > \*Originally posted by engineer\_comp\_geek \* > \*\*You need to make a conductive box out of the building. It doesn’t need to be solid metal. It can be metal with holes in it, as long as the holes aren’t bigger than about half of the wavelength. In other words, a metal screen will work just as well as cast iron, and wouldn’t be anywhere near as heavy. > > Do a little research on “faraday cage” if you want to know more about the theory behind it. \*\* A cage with 1/2-wave holes in it would be pretty lousy. At 1/2 the wavelength, there is almost no attenuation. Below this size, the attenuation increases by about 6 dB per octave. ---
**Author:** ![AskNott](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asknott/32/5790_2.png) [@AskNott](https://boards.straightdope.com/u/AskNott)\ **Post date:** [September 26, 2003, 10:29pm UTC](https://boards.straightdope.com/t/jamming-cell-phones/203937/7 "2003-09-26T22:29:12Z")
If the owner laid grounded metal window screen on all the exterior walls under the wallpaper, reception would be so crummy, nobody would use a cell phone in there. It wouldn’t be a perfect Faraday cage, but it would serve the purpose. ---
**Author:** ![Ms2001](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ms2001/32/18463_2.png) [@Ms2001](https://boards.straightdope.com/u/Ms2001)\ **Post date:** [September 27, 2003, 12:47am UTC](https://boards.straightdope.com/t/jamming-cell-phones/203937/8 "2003-09-27T00:47:05Z")
**Ryan Mahoney** , that cell phone jamming link is only for GSM. CDMA, a spread spectrum technology, is more common in the U.S., and it’s much harder to jam (which is why the military uses spread spectrum). ---
**Author:** ![Markxxx](https://avatars.discourse-cdn.com/v4/letter/m/5daacb/32.png) [@Markxxx](https://boards.straightdope.com/u/Markxxx)\ **Post date:** [September 27, 2003, 5:03am UTC](https://boards.straightdope.com/t/jamming-cell-phones/203937/9 "2003-09-27T05:03:22Z")
Asknott raises a good point. If you DO do some, say remodeling, do you have to make it so Cell Phones DO work. What if I just happen to use materials that would, not jam the cell phone but would make the reception so bad it would render them, effectively useless. ---
**Author:** ![St.Urho](https://avatars.discourse-cdn.com/v4/letter/s/8e7dd6/32.png) [@St.Urho](https://boards.straightdope.com/u/St.Urho)\ **Post date:** [September 27, 2003, 4:39pm UTC](https://boards.straightdope.com/t/jamming-cell-phones/203937/10 "2003-09-27T16:39:23Z")
If anyone is seriously thinking about doing this, please remember a few things. The frequencies used by cell phones are very close to those used by Emergency service radios and jammers can jam police, fire, EMS radios as well as cell phones. St. Urho EMT/Firefighter ---
**Author:** ![DougC](https://avatars.discourse-cdn.com/v4/letter/d/7feea3/32.png) [@DougC](https://boards.straightdope.com/u/DougC)\ **Post date:** [September 27, 2003, 11:24pm UTC](https://boards.straightdope.com/t/jamming-cell-phones/203937/11 "2003-09-27T23:24:32Z")
- - - I saw a story on a news site once (Slashdot, IIRC) that said that someone had found a way to make wood paneling with powdered metals in it that blocked cellphone signals both ways. They were marketing it to movie theaters, to stop people from using their phones inside. This story appeared maybe 6+ months ago… -Of course, in most locales/from a legal standpoint, passively blocking a signal from a particular location is legally a lot different frm actively transmitting a jamming signal. ~ ---
**Author:** ![drachillix](https://avatars.discourse-cdn.com/v4/letter/d/48db29/32.png) [@drachillix](https://boards.straightdope.com/u/drachillix)\ **Post date:** [September 28, 2003, 12:23am UTC](https://boards.straightdope.com/t/jamming-cell-phones/203937/12 "2003-09-28T00:23:17Z")
> [@](#): > > \*Originally posted by DougC \* > Of course, in most locales/from a legal standpoint, passively blocking a signal from a particular location is legally a lot different frm actively transmitting a jamming signal. True but for a variety of liability purposes it would probably need to be disclosed that the theatre/facility in question is radio shielded and that cell phones, pagers, etc most likely will not work. If they didn’t many people would not be able to do much movie viewing due to their often on call status. Sterner enforcement by theatre personell would probably be a more appropriate response than trying to actively or passively jam mobile communications.