Film-Tech Forum ARCHIVE: Cell Phone Jammer

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Posted by Jeremy Weigel (Member # 4208) on 06-13-2007, 12:07 AM:

Came across these schematics for building your own cell jammers if anybody wants to give it try.

http://www.cs.utah.edu/~chrisb/writing/jammer/circuit%20drawings/celljam5.pdf

Posted by Scott Norwood (Member # 30) on 06-13-2007, 07:02 AM:

...not FCC approved and not legal in the US...

Posted by Mark Gulbrandsen (Member # 72) on 06-13-2007, 07:46 AM:

Looking at the URL it appears to be the handiwork of someone at the University Of Utah. Illegal and if you happen to jam a doctors calls and something bad happens as a result [Eek!]

.

If you go into his site and read "Building The Cell Phone Jammer" he mentins the local electronics pacce I frequent... Ra-Elco. http://www.cs.utah.edu/~chrisb/writing/jammer/construction.htm

Mark

Posted by Louis Bornwasser (Member # 3063) on 06-13-2007, 08:02 AM:

Illegal ONLY IN US. Legal in Canada and elsewhere. In the USA, passive jamming (shielding) is legal and has been discussed here before. (Faraday screening).

It is possible that no one may know the difference in the real world.

Louis

Posted by Mitchell Dvoskin (Member # 751) on 06-13-2007, 08:46 AM:

Or you could buy one already built from England. The funny thing is they can't sell them in England, but I'm told by the person who gave me this link that they will happily ship them to the USA.

Posted by Paul Mayer (Member # 355) on 06-13-2007, 12:11 PM:

Even though the FCC says they're illegal at least one casino here uses jammers inside the casino cage area - no calls to or from cell phones while in the cage.

Nevada law also prohibits cell phone use within any sports book betting area or lounge. But rather than use jammers in such a public space, that law is strictly and immediately enforced by each gaming licensee's security staff. Violators are politely asked to cool it - if they don't it's fun to watch the consequent "bum's rush" treatment.

I like the idea of a private property owner being able to use a jammer to enforce public-access areas on that property where cell phones cannot be used (like inside theaters or airliners). If someone thinks it's so necessary to have their cell, they shouldn't be in that area. That's what off days or hours are for. Period.

Posted by Mark J. Marshall (Member # 1409) on 06-13-2007, 12:42 PM:

Amen, Paul.

I like the personal cell phone jammers that look like cell phones.

Posted by Mike Blakesley (Member # 26) on 06-13-2007, 01:00 PM:

I don't understand why it should be illegal to use one of these things if the business owner puts up a nice sign saying, "Your cell phone may not work in this building." If the all important people are given this advance warning, then why should there be a problem?

Posted by David Stambaugh (Member # 1102) on 06-13-2007, 01:10 PM:

Do the frequencies used by cell phones maybe overlap with (or are close to) those used by essential public services like police & fire?

Posted by Jack Ondracek (Member # 1466) on 06-13-2007, 02:08 PM:

quote: Mike Blakesley
I don't understand why it should be illegal to use one of these things

I'm with you on that. But I think it has to do more with political pressure from the cell phone industry and the sheer weight of monitoring regulations than anything else. There's always the possibility that jamming signals might find their way out of your building (the cell signals make their way IN, after all). That might be a problem for neighboring homes and businesses, and someone would have to come out to check. With the FCC having dialed back their enforcement divisions, that could be a real problem.

Much easier to just disallow the whole thing.

Louis is right, though. Passive jamming IS legal, and I doubt a doctor could have much to say about that.

Posted by Louis Bornwasser (Member # 3063) on 06-13-2007, 02:21 PM:

If I owned a multi screen theatre, I would passive jam as much as I could and then use a very low power jammer INSIDE the shield.

This would keep the jammer "IN" and the cell phone signal "OUT." If asked, I would just say that cell phones "never worked in here, even during construction." Louis

Posted by Stephen Furley (Member # 1277) on 06-13-2007, 02:38 PM:

quote: David Stambaugh
Do the frequencies used by cell phones maybe overlap with (or are close to) those used by essential public services like police & fire?

In the US mobile 'phones use frequencies in bands at around 1900MHz. and 850MHz., with 1900MHz. being by far the most common. (Over here we use 900MHz. and 1800MHZ., which is why tri-band or quad-band 'phones are needed if you want to use them in both places.

I think cordless 'phones are in the 2.4GHz. band, the same as 802.11b and g wireless networks. 802.11a is 5GHz.

I've no idea what police and fire use over there, but I'm somebody else will.

Posted by Frank Angel (Member # 248) on 06-13-2007, 04:31 PM:

Given that cell phones don't naturally work in many MANY places, no one is guaranteed, nor should they have an expectation that
they will be able to use their cells wherever they go, especially deep inside big buildings. I am all for the FCC dropping that stupid rule. Yah, I know, I know, there is an organizational culture in the FCC around the word "jamming;" just say the word and it automatically makes mucus shoot out of their noses. Just like there is a corporate culture in the studios that makes them have mini strokes when you mention DVD burning or worse, Public Domain. The FCC should just get over themselves and understand that American citizens also have a certain culture around being able to control what goes on in their own property without the government intruding with heavy handed regulations.

Besides, I think a doctor who has patients on the verge of death shouldn't be relying on very ify cellphone technology in the first place. In fact, he shoudn't even be peddling his ass out around town if things are so critical at the hospital. Would any of us buy the excuse, "Gee, sorry, but your loved one didn't make it because, well, I was out of cellphone range." What did doctors do before there were cell phones? Well, they will just have to do it again in my theatre....and in the subway....and in airplanes....and even in their own hospitals! Relying on cell phones for emergency situations? Do so at your own risk.

Posted by Daryl C. W. O'Shea (Member # 1303) on 06-13-2007, 05:36 PM:

quote: Frank Angel
The FCC should just get over themselves and understand that American citizens also have a certain culture around being able to control what goes on in their own property without the government intruding with heavy handed regulations.

Yeah but how many of those citizens, regardless of nationality, have the intelligence or the know how to contain RF jamming to their own property? How many that do would get kicks out of exceeding that limit and going "oops, sorry, didn't *really* mean to jam the entire town"?

Posted by Jack Ondracek (Member # 1466) on 06-13-2007, 08:14 PM:

... and so here we are!

Posted by Joel N. Weber II (Member # 3530) on 06-13-2007, 08:19 PM:

Indeed, one issue is that it's very difficult to prevent an active jammer from leaking outside one's property. Different phones will fail at different signal strengths, and the signal strength tends to fall off as the signal goes through a greater distance of air. So if you calibrated your signal to block all cell phones within your building, you'd likely end up blocking some cell phones outside your building.

You might be able to control where your jamming goes by shielding your building well, but if you do that, you might have a perfectly good passive jammer anyway.

I don't think the FCC's prohibiting jamming is likely something that was inspired by the cell phone industry; I suspect the rules go back to a time long before cell phones were common.

I believe there was a case within the last year or so when MassPort, the organization that owns some of the major airports in Massachusetts, wanted to be able to shut down other parties' 802.11 networks so that they could charge high rates for their 802.11 networks, and the FCC said that MassPort didn't get to control that.

Posted by Chris Slycord (Member # 4239) on 06-13-2007, 09:26 PM:

quote: Frank Angel
Besides, I think a doctor who has patients on the verge of death shouldn't be relying on very ify cellphone technology in the first place. In fact, he shoudn't even be peddling his ass out around town if things are so critical at the hospital.

While it's probably not exactly as you describe (the "on call" person is more likely the "emergency contact" in case the shit hits the fan or a rotating position for whoever is the extra worker in case they have a higher load than normal), I agree with the intent of what you're saying.

They give up the freedom of doing whatever the hell they want when they choose to take a job that has them being on call.

If that's too much, they should either find a job somewhere else or wait it out until they get enough seniority that they aren't required to be on call.

Posted by Daryl C. W. O'Shea (Member # 1303) on 06-13-2007, 11:07 PM:

That might work for the US (where a whole hell of a lot of Canadian doctors move to for the money) but up here I'd think most people would prefer to give up the ability to jam each other's phones (of which all doctors I know almost always have their phone's ringer turned off) rather than have them change to a better paying career (such as the manager of the local McDonald's) where they're not on call.

In many parts you could have 40 years more seniority than the other doctors and still need to be reachable. At this point, if you don't want them to be able to have a life so that they can always be near a land line, they're just going to choose to retire.

Posted by Chris Slycord (Member # 4239) on 06-13-2007, 11:42 PM:

quote: Daryl C. W. O'Shea
In many parts you could have 40 years more seniority than the other doctors and still need to be reachable. At this point, if you don't want them to be able to have a life so that they can always be near a land line, they're just going to choose to retire.

Of course, at some point they'd have to accept that a guy sometimes can't be reached.

Posted by Scott Jentsch (Member # 1681) on 06-19-2007, 11:11 AM:

The FCC gets involved whenever there is a device that emits signals on certain frequencies above a certain power (the interested observer may want to discover through independent research what quantifies "certain"). They're the same agency that gets bent out of shape if you attempt to start your own radio station by building a transmitter and doing your own "Pump Up the Volume" thing).

Any business that actively jams a cell phone signal without posting a notice about it could be held liable should that situation cause an incident where important and/or emergency communications were disrupted, especially through the use of an illegal jamming device.

Personally, I would avoid businesses that stated that cell phone communications were being purposely blocked. I use my cell phone so that I can be reached for important calls (such as our babysitter needing to reach us in case of emergency), and any business that would go out of their way to prevent me from receiving such a call would not deserve my business.

If a theater has a problem with teeny-boppers using their cell phones during a movie, then they should take responsibility for the enjoyment of the other patrons and get rid of the offenders.

Any theater willing to spend any kind of money and/or effort to install a jammer should be spending their money and effort monitoring their auditoriums instead. Word gets around quickly if you squash unruly and rude behavior swiftly and fairly. The teenagers will know that they can't get away with texting their friends in the next row, and the rest of us will appreciate your attentiveness and most likely return to your theater because of it.

Posted by Mike Blakesley (Member # 26) on 06-19-2007, 12:02 PM:

Scott - your post is well thought-out, however the audience needs to be educated to leave the damn cellphones home. These days, texting is much more bothersome than talking. It's impossible to have somebody pacing the aisles 100% of the time looking for blinking lights. I've found kids with their shirts pulled over their heads, texting.

Be that as it may, it's unnecessary to have a cell phone in a theatre for the babysitter to call you. I have been alive 50 years and I've never once heard of a kid dying because the parents were in a movie theatre and couldn't be reached.

Our theatre for the past 76 years has had a phone in the office. If there's a problem, a kid or a babysitter can call us and we will find the parent. We have a doctor here in town who loves movies. He never brings his cellphone with him. If the hospital needs him, they call our office and we go get him. He hasn't lost a patient yet because of the one minute it takes us to get him to the phone.

Of the thousands of phone calls I've fielded in my 28 years in the business, I can count on one hand the calls that were true emergencies, and even then I can't really remember ever having one that truly couldn't have waited until the movie was over. More often than not, it's the kids fighting over the TV remote, or something equally stupid.

I realize a bigger city would have more people and thus more potential problems, but people did without cellphones for the first hundred years of the movie business and they're NOT NECESSARY NOW.

Maybe I would feel differently about this if I were a parent. But I do remember when I was a kid, my parents went out every now and then. They always told us where they'd be, and we were strictly instructed not to call them unless somebody was bleeding to death or something equally dire. I have four younger siblings, and I can't remember our babysitters ever having to call our parents about anything.

Posted by Mitchell Dvoskin (Member # 751) on 06-19-2007, 12:08 PM:

The retailer's link that I posted on the first page of this thread also sells cell phone detectors. They are legal in the USA, and if installed by the theatre entrance would alert the usher/ticket taker that someone is attempting to bring a cell phone into the theatre. Of course, the detector would not work if the cell phone is off, but it would be better than nothing.

Posted by David Stambaugh (Member # 1102) on 06-19-2007, 12:13 PM:

FWIW since Regal switched to FirstLook for the preshow stuff here, with its multiple pleas to the audience to silence cellphones, I haven't noticed any actual cell phone use during shows. Once in a while I see people checking for text messages. No phones ringing though and no actual conversations. I suspect the education campaign or whatever you want to call it is having a positive effect.

Posted by Randy Stankey (Member # 64) on 06-19-2007, 01:56 PM:

I've been playing the Kyocera "Cell Phone Karma" spot in our threater before the show and have had ZERO cell phones ring in the last couple of months.

http://www.youtube.com/watch?v=qS2nZySpdhg

Not to say that I condone using "illegal" radio transmitters to jam cell phones but, what do you think about setting up a jammer to emit pules of RF every 30 seconds or so? The phone might ring but the person wouldn't be able to keep a call on-line long enough to have a conversation but would know that somebody is trying to reach him. If it was an important call, he could go outside.

Posted by Louis Bornwasser (Member # 3063) on 06-19-2007, 02:07 PM:

Remember, passive is entirely legal and yields the same result.

If you want active, maybe the "hearing impaired" guys could add an option to their existing boxes; flea powered for coverage in one house (or two) only. I know it's illegal and I don't care. Louis

Posted by Martin McCaffery (Member # 37) on 06-19-2007, 09:20 PM:

quote: Mike Blakesley
If there's a problem, a kid or a babysitter can call us and we will find the parent.

Ditto here. In the days before cell phones, the Drs would tell me they were on call and tell me where they were sitting. Seems to me multiplexes could hand out those vibrating pagers that chain resturants use if someone needs to be paged. Then they can go to the lobby and call.

Newest irritant for me, those 'berry Star Trek like ear cell phones. Apparantly, when you turn them off, the VERY bright LED blinks to let you know there's a call. A woman had one in her ear during the movie Friday. She didn't have a clue it was doing that, and graciously removed it when I asked her, but I'm sure there will be a-holes who will insist that everyone in the theatre must be aware of there presence at all times.

Posted by Mark Hajducki (Member # 1732) on 06-20-2007, 08:55 AM:

It should be possible to have directional blockers (possibly using more, lower powered transmitters pointing downwards)

A connection to the automation/ fire alarm system would be essential so as to allow use when needed.

----

Now where can we get a similar device for the human voice?

Posted by Mark J. Marshall (Member # 1409) on 06-20-2007, 08:59 AM:

I've seen cell phone jammers that only broadcast about 30 meters, and won't even penetrate glass. Those devices are perfect for theaters. Place them on the ceiling in the middle of the theater, and it would be good to go. I'm not sure how the FCC manages to claim jurisdiction over the broadcast airwaves in a privately owned room. This is the same puzzling phenomenon as the one where people say that it's illegal for you to receive a signal that comes into your house. If a satellite provider is beaming their signal into my home, and I manage to find a way to receive it in my home without their approval... how is that illegal? I know it is, but to me it doesn't make much sense. Of course in court, what makes sense to me doesn't matter much!

I agree that passive blocking works just as well, if not better because it blocks everything. But blocking everything passively is not the best option in case of an emergency. I would much rather have active jammers connected to the emergency fire control system so they can be programmed to be turned off in the event of an emergency. In our place, if the fire alarm goes off, all of the projectors stop. It would be just as easy to have the jammers shut down as well. You can't do that in a passive jamming environment.

Edit: Looks like Mark beat me by four minutes on that. Great minds think alike!

Posted by Daryl C. W. O'Shea (Member # 1303) on 06-20-2007, 04:21 PM:

quote: Mark J. Marshall
In our place, if the fire alarm goes off, all of the projectors stop. It would be just as easy to have the jammers shut down as well. You can't do that in a passive jamming environment.

Well... you could, and the explosions to make it work would be pretty cool.

Posted by David Buckley (Member # 2600) on 06-21-2007, 05:37 AM:

quote: Mark J. Marshall
I'm not sure how the FCC manages to claim jurisdiction over the broadcast airwaves in a privately owned room.

Firstly cellphones do not use "broadcast" airwaves, and secondly, they exert control by benefit of being granted power over all transmissions by your government.

The cellphone companies pay your government for the privilege of exclusive use of chunks of the frequency spectrum, and that exclusivity extends over a specified area. If you start up a service using those same frequencies (which is what an active jammer is) then you have trodden on the cellphone companies rights. Its not too dissimilar that you claim the privilege to watch a movie on your screen is granted by an admission fee.

As the old refrain says - use a faraday shield, and it all goes away. You could possibly use a jammer within a faraday sheild and not be transgressing any law, as long as you have no emissions outside the sheild, but if your sheild is that good then a jammer isn't necessary.

Or, get a Gavin. Gavin is an old guy who is one of our ushers, and he confiscates phones. He grabbed my son's phone one night, whilst I was in the booth, which I thought was hilarious, serve him right. The use of cellphones has decreased dramatically...

Posted by Scott Jentsch (Member # 1681) on 06-26-2007, 10:33 AM:

quote: David Buckley
Or, get a Gavin. Gavin is an old guy who is one of our ushers, and he confiscates phones. He grabbed my son's phone one night, whilst I was in the booth, which I thought was hilarious, serve him right. The use of cellphones has decreased dramatically...

That's what I'm talking about! [Smile]

My dad worked security at high school events when I was young and he never had many incidents to deal with. The kids knew he was there, but he moved around so much, they never knew just where he was. Incidents were handled decisively when they were still small, and word spread very quickly that stepping out of line was not going to be tolerated.

I went to a couple of dances that he worked at, and it was amazing how invisible he was. Just his presence was enough to keep the malcontents from thinking that starting a fight or other disruption was a good idea.

I think that any theater that practiced a little diligence in policing their auditoriums would soon gain a reputation for not tolerating rude behavior. The rude ones would either behave while they're there, or they wouldn't come in the first place because they know they won't get to see the entire movie anyway after they're caught texting their friends during the movie.

quote: Mike Blakesley
Our theatre for the past 76 years has had a phone in the office. If there's a problem, a kid or a babysitter can call us and we will find the parent.

Many theaters make it very difficult to contact a human at the theater. In the early years of The BigScreen Cinema Guide, I got a nasty phone call from Marcus Theatres Corp. because I was posting the voice phone numbers for the box office. Phone numbers that were publicly available in the phone book, in newspaper listings, etc.

The grip seems to be loosening a little on that, but it's still very difficult for someone to get a human on the phone at a theater when they need to. I think it makes much more sense for me to practice consideration for my fellow movie-goers by setting my phone on vibrate and leaving the theater if I do get a call that I have to answer.

On a side note, I went to see Pirates 3 last week, and a girl in the row behind me was getting "admonished" by a gentleman a couple of rows back just as the movie was starting. I turned around to see her with her feet up on the seat in front of her, texting on her cell phone. She knocked it off pretty quickly!