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Blocking Cell Phones in Church


GregS* writes ""Some Mexican priests, tired of Mass being interrupted by ringing cell phones, are using counterintelligence technology made in Israel to silence the devices." article

Soon to make its way north? pretty please?"


The radio jammers used in Mexico sound like the same technology employed by a private school in Italy to defeat text-messagers who were using cell phones to cheat on exams.

There are easier alternatives that won't create radio licensing problems. DefendAir(TM) Radio Shield Paint contains small whiskers of conducting material (the patent speaks of nanotubes) to create a low density Faraday Cage that reduces radio transmissions in the cell phone frequency range to the point that people can neither send nor receive while inside the painted room. The technology is protected by patent (6,576,336 Electrically Conductive and Electromagnetic Radiation Absorptive Coating Compositions And The Like), so there's some science involved. The only sales outlet I could easily discover was at

This is not an endorsement(!). More than a few of us, however, would be interested in learning if it really works. One gallon of paint is claimed to cover 160 square feet.

I think the FCC should change the rules so that you can jam on your own property. If a movie theater wants to jam cell phones they should be allowed to do so as long as the jamming does not extend bryond the bounds of their property. The same goes for libraries.

I hate cell-phones. Never use one. They are very suspect...they may contribute to health problems and I've already had enough of those. Hate to see drivers zooming down the highway using one. Hate to see two people walking down the street together, each talking to SOMEONE ELSE on their cellphone. Hate to hear someone walking up behind you and you think they're calling out to you and they're actually talking on their cellphone. Ah, for the old days when you had to find an empty and working pay phone.

I used to not be too fond of them... then I got into a car wreck five hours from home, in another state, in the absolute middle of nowhere. I was certainly glad of their existence then; there were no pay phones anywhere around. I'm never without mine now, although I don't really use it much.

Well, that's okay then. We'll let you have one. :-) The only reason I'd have a cell phone is for the reason you described--car wreck in the middle of nowhere or some other kind of emergency. It's not the cell phones that are bad; it's the people who use them at inappropriate times: in libraries, movie theaters, restaurants, etc... Many times I"ve wanted to walk up to somebody and smack the phone out of their hand. And then smack the person.

As a duly-licensed amateur radio operator, I will say that jamming cannot really be confined within the bounds of a property. Such will not be able to work. Unless the laws of physics get radically changed, RF energy is going to radiate unless it is blocked by some sort of shielding. It would be cheaper just to work during any major shifting/renovation operations to rearrange one's metal shelving around to create a faraday cage to block the signals. No laws are broken. It looks neat and it accomplishes your purpose without doing something that could be potentially life-threatening. Jamming is bad no matter what. I do not want the blood on my hands from any leaking jamming signal (which will occur as far as radio propogation physics is concerned) if I jammed someone's 911 call...

In a library, judicious placement of shelving allows the same thing

I hate the cell phones in the library as much as the next person, but there are legitimate reasons for those and pagers (if you're on-call, have a sick family member, pregnant significant other). Easier than the paint is the wire mesh in the walls, but that has to be done ahead of time also at great expense. Jamming the signals is probably not within FCC rules (as is proper). There was a NYTimes article in Circuits 4/8/04 and also a really nice article in Communications Engineer (by IEE) by Newbold called "Designing buildings for the wireless age" (v2 n3, Jun-Jul 04): 18-21. It talks about "frequency selective surfaces". I think we need to modify the behavior, instead of the buildings or equipment!

Using the (presumably metal) shelves could work, but not as well. Cecil Adams remains one of the best at translating technobabble into plain language, and I recommend his article on how the glass doors on microwave ovens work (see l).

The wavelengths that apply to cell phones are about ten times longer, but the key to making any Faraday cage work is making the mesh size smaller than the wavelength. Also, the signal doesn't need to be blocked completely, just reduced a bit. If you have access to students, turn this into a science fair project. You could generate an interesting backlash effect by having armies of small children wandering through the stacks muttering "can you hear me know?" into Mommy's cell phone, and recording their findings on a floorplan.