back to article Jamming convicts' mobiles works

On Friday CellAntenna demonstrated it could jam mobile phones within a 1000 square meter area within a prison, without noticeably affecting those passing. This opens the door to widespread adoption of the technology. The test took places at the Lieber Correctional Institution, at the request of Jon Ozmint and in the presence …


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  1. Anonymous Coward


    Jamming convicts' mobiles works.


    i.e. Jamming the mobile phones of a number of convicts is successful

    I had to read the story before the

    Come now El Reg and I'm dyslexic

  2. Simon Rockman

    Depends who is doing the jamming

    In the UK you need to own the spectrum to transmit on it. The UK networks could operate a jammer on behalf of the prison.

  3. Anonymous Coward

    And in the UK?

    Do we do that here? I don't think so but we should. I bet the crime rate will plummit if we do

  4. Will Leamon

    For the love of cupcakes!

    Please install these things in movie theaters!

  5. Anonymous Coward

    Granular blocking already possible

    I saw a demonstration of a system that used 3 antenna to triangulate a mobile signal to within 5m in a known area. As these are all digital communications, it grabbed the IMEI of the device, displaying its location on a display. Obviously, given the IMEI, the prison service could simply pass this info on to the phone service providers and request that they block this device. Then the phone is useless, even if they get a new SIM in it.

    If they manage to get another phone, as soon as it registers, the IMEI is captured and disabled again. Very simple system, easy to manage the coverage of it, and no jamming required. If the phone companies buy into the PR value of it, they could automate the entire system.

    Nice big signs at the entrance to the prison to say "Turn off your phone before entering, otherwise it will cease operating". They could even include a whitelist of their own phones if they need to use them inside the building.

    AC because I'm not sure how legal that sort of triangulation is these days. The odd Terry Wrist could make use of it I suppose.......

  6. David Webb


    Won't happen here, soon as anyone tries it on a prison the overpaid human rights lawyers would be on it in a flash "your honour, I'm getting paid a fortune just to be here, lets drag this case on till after the economic downturn so I don't skip any payments on my ferrari please".

  7. Anonymous Coward
    Anonymous Coward



  8. Anonymous Coward
    Anonymous Coward

    jamming the prisoners?

    Doesn't that happen already? *rimshot*

    "But, won't somebody think of the criminals!" -some random bleeding heart, or someone with commercial gain from criminal communications.

    I have a better idea. have a powerful transmitter that waits idle until it detects the signal of a cell phone checking in with a tower, then hitting that area with a kilowatt or two and smoke the phone. Preferrably the crook who's got the mobile kiestered will be jumping around for awhile.

    Film that and sell a compilation on DVD to pay for the hardware.

  9. Nigel Bird

    Spectrum is owned by....

    In the UK the Government owns the spectrum, the operators rent it for for large sums of money and normally fixed periods. Their license dictates what they can do with it.

  10. Peter

    I'd have one...

    I'd use one anytime I was on a bus or a train, provided it was pocketeable.


  11. Chris
    Thumb Down

    why is this even necessary?

    Surely convicts are not allowed to have "cell" phones in the first place? Yes, they might be able to smuggle in a small one in a bodily orifice, but how long will the battery last? I'm guessing a charger would be a little bit harder to conceal, and electrical outlets are fixed in position and probably well monitored as well (or they would be in any prison *I* owned).

    Keeping every prisoner inside a Faraday cage should achieve the same effect, and that could double as a prison cell also. How many of those can you build for $150k?

  12. Anonymous Coward


    might save me a fortune in all that tin foil

    do they do a mobile version ;p

  13. Henry Wertz Gold badge


    "Why else would they have [radio masts] pointing at prisons?"

    Because the FCC licenses have a clause that if you don't cover an area, you can lose the license for it. Also, some prisons are off in the middle of nowhere, but some are just in some city, so it's not pointing at the prison, it's pointing in general in that direction.

    If these prisons are out in the desert or whatever, this is fine with me. But they HAVE to make sure they are not interfering with neighboring stuff. Note, just because the phone "works" outside this zone doesn't mean there isn't interference -- WCDMA and CDMA are interference-limited, having an artificial interference source could severely degrade the capacity of these systems... requiring the cell co (if they can't get the jammer shut down) to add cell sites and add capacity to existing sites when they otherwise wouldn't have to. Your phone bill could be raised because prisons are interfering with your signal!

  14. Franklin

    Going about it the wrong way

    Just stick some copper mesh on the walls of the area where you don't want cell phones to work, ground it, and wham! Instant Faraday cage. Cell phones quit working. A lot cheaper than what they're talking about, too, and no pesky laws being violated.

    I'll take my $150,000 consultant's fees now, kthx.

  15. Anonymous Coward

    Don't tell the french

    The french are known for locking people up without cause and without notifying the consulate or the family of the prisoner (at least in this house).

    A corrupt guard who permited prisoners to receive calls on the guards personal mobile was the only way we (as family) managed to find out - after he'd been inprisoned for over 2 weeks!!

    Of course, if they were to block the mobile signals, we probably wouldn't have found out and he'd still be locked up at the mercy of the froggy legal 'system'.

  16. Mike Richards Silver badge

    First amendment?

    An interesting defence - use of the part of the Constitution that guarantees your free speech to deprive people of theirs. Gotta love the First Amendment, it's pretty much good for any purpose - if only we had something similar over here on the right-hand bank of the Atlantic.

  17. Anonymous Coward
    Anonymous Coward

    Pump Up the Jam

    I believe it's illegal for prisoners in the UK to possess mobile phones. They've been several cases where they've been used to order murders on the outside. This technology should be installed ASAP.

  18. Neil Stansbury


    This is easy - just wrap the prisoners in chicken mesh.

    DIY mobile phone blocking Faraday cages - Done!

  19. Winkypop Silver badge
    Thumb Up

    I've come late to this story..

    ...are we proposing the locking up of all mobile phone users?

    [fingers crossed]

  20. Andy Worth

    Better solution in the UK....

    They just need to invent an electrical field which can make mobiles explode. Prisoners here are not supposed to have a mobile phone anyway, so it (according to a prison nurse I knew) is quite common for them to be stored up the ass. Exploding the phones whould sort out the population issue in prisons.

    If that is too extreme for you, a field which forces phones to ring. Then you just look for the prisoner whose ass is playing the Nokia tune, or vibrating steadily with a very pleased look on his face.

  21. Anthony Mark

    Just build giant faraday cages over the prisons

    More environmentally friendly as it's passive and doesn't consume energy once it's in place.

    Can also be used on cinemas, theatres, museums, public transport, etc.

  22. Anonymous Coward
    Anonymous Coward

    Faraday cages

    For all you smart Alecs, it's a lot harder to build a Faraday cage which is effective at blocking mobile phones (900MHz/1800MHz) than you think. If you're in an area with a reasonable signal strength, a mobile will often still work when shut inside a (non-operating) microwave oven... (many dB attenuation, but still enough gets in/out). You'd need a mesh that's finer than your average prison bars, and lots of gold-plated fingers around all the door seals. Would cost a lot of money, and wouldn't last long in a prison environment I'd guess.

  23. Tim Hughes

    Faraday Cages could be a problem

    ... because they would prevent any radio signals getting through - like the one the guards need for their comms equipment. Specifically jamming telephone frequencies does seem like a better bet.

  24. Andus McCoatover

    @ Tim Hughes and Faraday cages

    <<because they would prevent any radio signals getting through - like the one the guards need for their comms equipment. >>

    Not necessarily a problem - the guards need communication between each other, *within* the faraday cage. To get out, why not use POTS?

  25. Mike Groombridge

    i'm sure this is old tech

    my college jammed all mobiles in are computer suite for about a year until some (tit) one complained. the commputer suite was meant to be a quiet ( as quiet as 200 pc's can be ) so no phones any way but because it extended two metres beyond the door he moaned and they turned it off the irony being he started making calls from the computer room and so they confiscated his phone and locked him out of the computers for 2 weeks as the rules allowed and you try being a computing student when you can't log onto the computer

  26. Oliver
    Paris Hilton

    Surely this would be legal in Blighty!

    If prisoners aren't allowed mobile phones in prison and they can get away with this under EU Human Rights legislation, how would it be illegal to actively block illicitly procured mobiles within the premises?

    If there were a law specifically addressing blocking of signals surely a small amendment would take care of this - there would surely be certain exceptions provided for anyway. As has been mentioned there have been some well documented and fairly horrific crimes arranged or abetted by the use of mobile phones in prisons.

    Paris, do you think she smuggled her mobile in?

  27. Anonymous Coward
    Anonymous Coward


    I've never been in a prision, I expect guards have walkie-talkies or whatever, but I'm just wondering what would happen if a guard was locked into a cell and couldn't use his mobile phone to call for help?

    If networks know where you're calling from when you make a call - can't they just check your not calling from within a prison and aren't a guard and refuse to connect or send the text message?

  28. Anonymous Coward

    This isBasic

    How about have a mini / pico network that they roam on but block cetain calls and monitor the traffic for intellegence purposes. Perhap ban incomming calls, filter text messages.. etc...

  29. Danny Silver badge

    Won't cut crime

    In the UK staff patrol with handheld scanners. The prison service probably gain quite a lot of intelligence from prisoners 'secret' phonecalls so it is not apparent that jamming would cut crime. Jamming would inevitably lead to complaints from prisoners and staff who are, or claim to be, electrosensitive.

    Any gangster who wants to get information in and out of prison is not reliant on mobile phones, they can just tell a visitor or even by letter 'in so many words'.

    One simple way to cut mobile phones in prison is to normalise the payphone rates in the prisons.

    The normal prison telephone rates are prohibitively high for many prisoners, which isolates them from their family and makes organising an appeal nearly impossible. This is because large parts of the prison service are privatised, including the virtually unpaid work the prisoners do, the caterering contracts and the telephone contract. By lowering the cost to prisoners of controlled payphones the value of smuggled mobile phones drops.

    Off topic, but I do not believe it is just to profit from someones imprisonment, if a judge wanted to financially punish a prisoner then it should be part of their sentence. I think any state that sentences people has a duty to imprison them itself, not subcontract it to the highest bidder.

  30. Delboy
    Thumb Up


    I'm with you, although I favour the reintroduction of capital punishment for owning a mobile phone.

  31. Stevie


    Please can we have one of these in my local cinema next?

    [Franklin] You can't have your fee because you forgot to factor in the sky-high price of copper these days. All the money was spent on mesh. They had enough to do a single car garage.

  32. Anonymous Coward
    Anonymous Coward

    Re: Faraday cages

    Whilst they are hard to make perfect, there are certain companies who do indeed employ shielding that cuts out the majority of outside signals. You can still find certain parts of buildings where you get a signal, but for a prison it would probably be easy to cut out all the cells. Just leaves outside when they exercise/whatever, but surely easy enough to search them and also spot when they're on the phone.

    But yes, it does cut out other radio signals too.

    Would surely be cheaper though that a jamming signal, especially considering the prisoners could probably sue for harmful effects of such a signal (especially in America).

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