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France to Allow Cell Phone Jamming
ZuperDee writes "According to this article, the French industry minister has approved a decision to allow cinemas, concert halls and theaters to install cell phone jammers, on the condition that emergency calls can still get through."
No, GSM jammers of this type work by impersonating the local base stations by responding before them, but not actually letting anything through.
The systems have been available for a few years,
and are apparently very good at blocking out only a well defined area. The stumbling blocks have been entirely legal/regulatory.
I don't know if the available equipment handles it already, but there is no technical reason why the jammer couldn't engage slightly more thoroughly in the transaction and forward select calls.
sudo ergo sum
Is it really necessary to be reachable while you're at the cinema ? No. And if it is necessary, you shouldn't be at the cinema.
- Leon Mergen
http://www.solatis.com
The only thing that comes to mind is having a special node at the theatre thats essentially a repeater (but doesn't ring the phone or allow outgoing calls to be made). Calls to anyone with a phone from a certain prefix or list of numbers (given to any emergency responders) is allowed through. Think of it like a cell-phone firewall.
If that's how they're planning on doing it I don't know. But there has to be some way of distinguishing emergency calls, or emergency cell phones from normal everyday calls/phones.
AccountKiller
There's actually two factors at work here - digital cell phones attenuate their transmit power level based on the strength of the signal they receive. The theory is that if they are receiving a strong signal from a cell tower, they must be very near it physically, so they don't need to use as much power to transmit and be heard by the tower. So the first thing they do is set up a local base station; all the phones will lock in on it because it is the strongest signal around, and they will all reduce their transmit power because the local signal is so strong. So this automatically means your phone will only use the local base station, no other cell towers will be able to hear the weak signal your phones will be putting out.
The region being affected is easily controlled using directional antennas. Most cell towers already use a 120 degree beam spread, so directional antennas are the usual already, but they can certainly use a narrower beam antenna if they want.
As for routing emergency calls, again, the network tells the phone what the phone is allowed to do. No problem there...
-- *My* journal is more interesting than *yours*...
Trivial. The same way that you handle calls in a large shopping mall or other localised concentration of people. You setup a micro-cell. The difference is the one in the cinema will only route emergency calls; the rest get a recorded message saying "fuck off you sad bastards: try watching the film." QED.
Bad analogies are like waxing a monkey with a rainbow.
You can control the affected area even more precisely than that: if you have two or more antennas, you could triangulate the position of a phone and choose whether to service it or not based on its position. Meaning that you can literally draw your block-zone on the map and when you step outside that invisible line, your phone works. (Not sure they actually do, but it's certainly possible.
This also means you don't have to drown out any other transmitters, you can just play man-in the middle: you know which phones are in your zone, if a tower tries to contat it, you say you're it, but can't answer. If a phone tries to contact a tower, you pretend you're it an denies service. All you have to do is be first.
Combined, you have a very robust soloution with a well-defined virtual cage that is "invisible" from the outside but completely "dark" on the inside.
sudo ergo sum
A lot of people are missing the point.
Emergency calls OUTSIDE, people.
RTFA man, it says
"Devedjian specified however that emergency calls and calls made outside theaters and other performance spaces must not be affected."
It says nothing about emergency calls OUTSIDE.
You'll have that sometimes...
I think that this is great. I'm a classically trained musician and a sound engineer so I spend a lot of time either performing or recording concerts. When I'm onstage, I'm already a bundle of nerves and have to concentrate like hell for fear of messing up. Whenever I hear a phone go off, it is very distracting. I can ignore it and carry on, but it does throw you for a moment. 99% of the time it won't result in any audible wobble, but if it happens at the wrong time it can throw you completely and you screw up bigtime. When I'm recording, it is even worse. Even if somebody has their phone on silent but are sitting close enough to some of the gear, you can get the lovely du-du-du-du, du-du-du-du, du-du-du-du-duuuuuuuuuu sound captured in your recording. Again, this happens very rarely, but when it does I have to be physically restrained... I also lecture at a university - whenever students use their phone in class, it shows a distinct lack of respect for me and for the other students, some of whom are finding it difficult enough to follow the course content as it is.
faraday cage in the theatre, and a GSM picocell that only routes emergency (i.e. 911 or 112 in Europe) calls going OUT to the emergency services - everything else blocked. This is pretty easy: the same thing is effectively happening (albeit without the trivial faraday cage - an earthed liner of chickenwire behind the wall coverings will do this) everytime your GSM phone says "SOS calls only" on the display - it's telling you there's a GSM network nearby, but (usually because your phone provider doesn't have a roaming agreement with that network provider) you can't use it, bar emergencies.