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Cheap Cell-Phone Detector 296

An anonymous reader contributes a link to a BBC News article on a cheap cell-phone detector created by six New Zealand high-school students for a business competition, excerpting "The detector, which they have called CellTrac-r, works by picking up the bursts of radio frequency activity that emit from a mobile each time it sends or receives a call or a text message. The device can detect these bursts of electro-magnetic energy up to a radius of 30 metres. It can also measure the amount of the energy to determine the distance of the mobile.", and noting "Seems like a perfect /.er hack project, and as initiator I get 5% of gross profits."
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Cheap Cell-Phone Detector

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  • Neat, Now if only (Score:5, Interesting)

    by novalogic ( 697144 ) <> on Wednesday July 21, 2004 @04:00AM (#9757510)
    ... I can tie it into a cellphone JAMMER on my car, so I can detect moron drivers on phones as they come close, and jam them when they become a danger.

    I can see police cars equipted with this kinda stuff in places where Yack and Drive is illegal.

    These kids are rich.
    • by sr180 ( 700526 ) on Wednesday July 21, 2004 @04:01AM (#9757518) Journal
      Great, so they look at their phone to work out why it dropped out right as they swerve their vehicle into you..

    • by Osty ( 16825 )

      ... I can tie it into a cellphone JAMMER on my car, so I can detect moron drivers on phones as they come close, and jam them when they become a danger.

      Because the previously inattentive driver wasn't enough a danger, now you have a confused and angered driver more concerned with why his cell phone stopped working than paying attention to the road?

    • We wouldn't want you to be the car that rubbernecks the scene of a heinous car wreck where people are trying to dial 911, possibly working through procedures to save a person's life.
    • by Albanach ( 527650 ) on Wednesday July 21, 2004 @06:02AM (#9757897) Homepage
      I can see police cars equipted with this kinda stuff in places where Yack and Drive is illegal.

      I don't drive, though I'm often a passenger in cars. I'm often a passenger on buses too, strange as this may sound to some North Americans. In both situations I'll frequently use my mobile phone - are the police really going to start tracking vehicles and trying to establish if there's more than one occupant? What about single occupant cars with a proper hands free kit installed? What about sensible folk who when driving ignore the fact their phone was ringing and let it divert to voicemail? I really can't see the police wasting much time with this.

      • What about single occupant cars with a proper hands free kit installed?

        No such thing.
        It's not the hands that are the problem, it's the brain [].
        • Ah, so we are going to outlaw any conversation in a vehicle? What about children, I know mine can be quite distracting. And how about eating, drinking, applying makeup, etc. The fact is we should REALLY be working on having cars drive themselves because it's something people do VERY poorly statistically. We didn't evolve to pilot a vehicle moving at 60+mpg, we evolved to stalk prey on grasslands, quite different sets of requirements. Just because drivers on cellphones are the pet peeve of the year doesn't m
          • "We didn't evolve to pilot a vehicle moving at 60+mpg, we evolved to stalk prey on grasslands, quite different sets of requirements."

            What planet are you living on? We did evolve to drive 60 mph machines. Look: we've evolved, and we drive cars. Simple as that. Did we evolve to live in houses? To use computers to find unimaginibly large prime numbers? Did our fingers evolve to type on keyboards so that we might communicate on /.?

            Just because certain people are lousy at it doesnt mean that it's a problem
          • What about children, I know mine can be quite distracting.

            That's why cars have trunks.

    • With a large enough noise generator (power-wise) and antenna, you could cover a nice big area - who needs to say it's legal. (see this [])

      Also, this device these kids are touting is nothing new. A google search will reveal various circuits schematics for cell phone detectors.
    • Now when my phone is in the glove box and someone trys to call or sends a text I'm going to get arrested.
    • they might also try this at hospitals where they ask you to turn off your phone so that you dont interfere with x-rays and pacemakers.
    • Does anybody know of a simple design for a cell jammer?

      Every day I want to jam idiots who commit DWT. If some asshat is sitting still at a green light, you can make book that his/her head is cocked to the left...

      A 150-300 foot circle of silence around my car would be perfect.
    • I can see police cars equipted with this kinda stuff in places where Yack and Drive is illegal.

      This type of law enforcement, like speed limit enforcement, will be primarily for the purpose of revenue generation. Cell phones in vehicles are not the problem, inattentive drivers are. And it doesn't matter what the source of the distraction is. Besides, what if the passenger is using a phone? No politician would suggest that passengers and drivers both cannot use cell phones in a vehicle.
  • by Flerg ( 152285 ) on Wednesday July 21, 2004 @04:00AM (#9757511)
    Why would you want to detect cheap cell phones?
  • Already have one (Score:5, Informative)

    by shird ( 566377 ) on Wednesday July 21, 2004 @04:04AM (#9757524) Homepage Journal
    I already have one, its a set of speakers on my desktop. Everytime a cellphone gets a call/text i get a:


    Also useful for knowing when Im about to get a call and can start looking for my phone well in advance before it starts ringing.
    • Re:Already have one (Score:2, Interesting)

      by jlanthripp ( 244362 )
      That happens to me too, though I'd use a different word to describe the sound. I don't get a dick every time I get a phone call...still have the one I was born with :-P

      Also interferes with the home stereo, the television, etc. - pretty much anything that involves an audio amplifier and speakers. And it does it every now and then, maybe every 5-10 minutes, call or no call.

      This is with Cingular, on GSM. And the service sucks too, dead zones all over the place. Fuck GSM, give me back my CDMA!

    • The GSM phones do this over our desk phones
    • I was going to suggest my monitor.. you get little fuzzy horizontal lines at random places... The benefit here is that it only does this when i'm about to get a call or an sms rather than when its just loggin onto the cell..
    • "dicky-dick-dicky-dick-dicky-diiiiiick"

      How many dicks is that?

    • That happens on our telephone and TV as well. More of a soft popping sound.
    • I already have one, its a set of speakers on my desktop. Everytime a cellphone gets a call/text i get a:


      Yeah, me too, but it's not only during a call or text. Apparently, my phone (a Nokia 6340i on Cingular) periodically contacts the network -- either it's auto-setting its clock or just checking in with Big Brother. For a while, at first, I had no idea why I was hearing these weird little chirps from my speakers, until I noticed they also happened right before I re

  • Finally! (Score:5, Funny)

    by WegianWarrior ( 649800 ) on Wednesday July 21, 2004 @04:05AM (#9757528) Journal

    ...a great way to find my cellphone those times when I put it on silent ringing and then forgets where I put it down :) (don't laught - it happens more often than I like to admidt). Now, if they could also find a way to indicate not just how far away the mobile phone is, but also in what direction... shouldn't be hard - either a directionloop, or two antennas 90 degress apart.

    • How do you get 2 antennas 90 degrees apart? Wouldn't you need THREE points?
      • by WegianWarrior ( 649800 ) on Wednesday July 21, 2004 @04:22AM (#9757602) Journal

        I often make the mistake of assuming people know what I know... in this cause, how most modern ADF (Automatic Direction Finding) equipment work in aircraft... Mea culpa =)

        A coiled antenna - also know as a directionloop - recives the signal strongest when the 'open end' of the coil points towards the transmitter. If you have two coiled antennas, one orientated dead ahead (in relation to you) and the other pointing left-right (ie: being 90 degrees apart), it is reasonable easy to use the difference in signal strenght to figure out the direction the source of the radiotransmitter - in this case the mobile phone.

        Three points (or antennas) would be needed if you want a fix on the radiotransmitter (mobile phone) and not just the direction.

    • Right. And what makes you think you'll be able to find your cell phone tracker when you lose your phone? I bet when you buy one of these you'll end up finding both the tracker as the cell phone on the bottom of the laundry bin after a 4 hour search.
  • by darnok ( 650458 ) on Wednesday July 21, 2004 @04:05AM (#9757530)
    So this thing can detect a mobile phone only when it sends or receives a call or text message? I'm not that smart, but I figure that would tend to coincide with either the phone making a ringing or beeping noise, or someone talking into it.

    Hmm, how could I possibly detect this using attachments I've had on my head since birth ...?
  • reliability (Score:2, Interesting)

    by dncsky1530 ( 711564 )
    If it can pick up cell phones in a 30 metres radius, one would have to think that in a conjested area, it may pick up many cellphones and possibly confuse the system. Also I would like to know if this device could interfere with peoples mobile calls, if so, cell phone jammers [] (this one isnt pocket sized) are already avaialable.
  • This is news? (Score:4, Interesting)

    by Captain_Chaos ( 103843 ) on Wednesday July 21, 2004 @04:10AM (#9757545)
    Come on! We've been getting these for free with our Coke and popcorn for years. I've a small green Heineken bottle that lights up when my cell phone is active, and also a pen with a little red light at the end which does the same.

    There's even ones that don't need batteries and work solely on the energy that's broadcast by the phone (although these have to be attached to the phone so they're not much good as "cell phone detectors"). All of these have been around for quite a while (or at least they have here in Europe).

    • Whenever my cell phone rings it lights up. But i guess these guys extended the range to 30 meters, rather that standard 2-3 meters you get. Which basically means that in a crowd with around 50 cell phones around you, even if none of them are ringing this device will light up. So not much use as a tracker in such conditions.

      But think of buildings collapsed during earthquakes. May be helpful there!

      • ...........yes.

        The first thing that ppl worry about after a building collapse is finding their mobile phones :P

        (come on, i know MY mobile is more important to me that human life!!)
    • Re:This is news? (Score:3, Insightful)

      by tfb ( 49770 )
      This isn't the point of these things. As lots of people have pointed out, It's pretty easy to detect a phone at short range, as anyone with any kind of small-signal audio system (microphone amplifier, probably even line-level things or higher) can tell you. In fact the first phone I had used to make my (CRT in those days) screen flicker when it was close enough.

      But that's not what these things are for. There are plenty of environments where you are *not* meant to have mobiles turned on because: inside p
      • I still don't think it's a big deal. Those gadgets I was talking about that I have, they light up when I'm 10 m away, and they cost next to nothing. It can't be that difficult to make them work at 30 m and even if that increased their cost a hundredfold, they would still be cheap.
  • by worf_mo ( 193770 )
    I remember that a couple of years ago you could get a sort of pen that would light up whenever somebody within a certain range (a couple meters) was using his cell phone. The CellTrac-r described in the article sounds like a similar gadget, with possible extra capabilities (like determining the distance).
  • mobile power output varies and is controled by the phone, you can't derive distant by looking at power output.
  • Its easy (Score:5, Funny)

    by FraggedSquid ( 737869 ) on Wednesday July 21, 2004 @04:12AM (#9757557)
    Just listen for somebody shouting "I'M ON THE TRAIN!". As if we didn't know already.
  • by Lord Kano ( 13027 ) on Wednesday July 21, 2004 @04:17AM (#9757580) Homepage Journal
    so that the MPAA goon squads can kick your out and confiscate your phone before you can text all of your friends and warn them not to waste their money of whatever shitty movie you had the misfortune of seeing first.

  • by GrpA ( 691294 ) on Wednesday July 21, 2004 @04:18AM (#9757586)
    Just think about it.

    Give it 4 or 5 years, and mobile phones on new generation networks will have high resolution image stabilised digital cameras and the ability to transmit this image in real time, already compressed, down multi-megabit networks.

    Such a phone would video a movie from a pocket, and there would be no evidence, because it would be transmitted away.

    So there is a huge value in these detectors...

    Just remember to leave your mobile at home when you visit the cinemas, or having it ring during the movie will only be the start of having a very very bad day...

    •'re still going to need a damn camera, and be filming with it. I doubt they'll be able to integrate that in the phone with a usable quality, and even if they did it wouldn't be in your pocket. That would pretty much be a give-away even if there's no recording. Combined with some testimony from whoever caught you, I don't think the defense will fly...

  • Cell phone noise (Score:2, Interesting)

    by Caltheos ( 573406 )
    Hardly a new idea. as a commercial device a bit odd and of dubious use. I know my phone, nokia 3595 i think, makes any amp;lifiers near it buzz loudly when its updating the clock or receive calls. obviously some phones are more suceptible to being pick up then others.
  • I remember (Score:3, Informative)

    by lachlan76 ( 770870 ) on Wednesday July 21, 2004 @04:39AM (#9757677)
    I've seen something similar to this before []. This one however is slightly different (there are two ICs in the one from the article. For those who don't understand electronics, the incoming signal goes into an operational amplifier, and this will compare the incoming signals with that of a fixed voltage (from a battery). This then drives a MOSFET (like a transistor) to switch a load on and off. I would guess that the second IC in the new device is to measure the distance (v x == close) from the signal level). I build the circuit in the PDF, and it has a range of a few meters, but could be improved, if you had the parts/time.
  • Technical article? (Score:3, Insightful)

    by europrobe ( 167359 ) <> on Wednesday July 21, 2004 @04:59AM (#9757728) Homepage
    I would assume that this device can also detect when the cell phone does its intermittent "reaffiliation" with the network, since (as others have pointed out) you would otherwise only be able to detect it when it's in use. At which point I wouldn't really need this detector to find out that they have a cell phone.

    I do find it strange that they can detect the range to the mobile phone just by using the signal strength. All network standards worth mentioning include the ability for the transmitters to adapt their power depending on the signal strength at the receiver, so signal strength is not a good indicator of distance.
    • by numo ( 181335 )
      I would assume that this device can also detect when the cell phone does its intermittent "reaffiliation" with the network

      Yup - normally it does it every few hours. It is possible to force the phone to do this - just jam the frequencies causing it to lose the network. Of course, this would be illegal, as this is a licensed band.

      All network standards worth mentioning include the ability for the transmitters to adapt their power.

      AFAIR at least GSM uses the full power when negotiating with the network -
  • Ears (Score:4, Funny)

    by tiredwired ( 525324 ) on Wednesday July 21, 2004 @05:01AM (#9757735)
    Ears are so cheap I got two of them. I can detect cell phones quite well.
  • by TheOtherAgentM ( 700696 ) on Wednesday July 21, 2004 @05:11AM (#9757769)
    That way you know where the phone is when you get messages or calls. It's always funny to me when the phone rings and someone yells, "Phone!" That's why it rings in the first place.
  • by SmoothTom ( 455688 ) <> on Wednesday July 21, 2004 @05:25AM (#9757811) Homepage
    1) It might detect a cellphone being used for sureptitious evesedropping on a conversation

    2) It might detect a cellphone in a silent text ony mode receiving test answers

    3) It might detect an active cellphone in a secure environment where they are prohibited

    Not all potential uses are obvious ones.

    Consider the prison example from the article (You did RTFA, right?) - if prisoners are prohibited cellphones and you detect one in use in a cellblock, it is time to do a detailed search...

  • "Seems like a perfect /.er hack project, and as initiator I get 5% of gross profits."

    How about.. no.
  • The fact that such detectors give out a strength reading that can be used to determine distance gives the opportunity for three or more to be used together in a theater setup. A phone wouldn't even have to ring, just the session establishing contact with the towers is enough, at which point the circles could be drawn to find their intersect point and they'd know where to send an usher to prevent the mid-show interruption before it happens.
  • by Fizzl ( 209397 ) <<ten.lzzif> <ta> <lzzif>> on Wednesday July 21, 2004 @06:47AM (#9758033) Homepage Journal
    Very handy for hospitals whose equipment can potentially be sensitive to the high interference caused by cell phones. (Not going into if they actually are, but when someones life is on line, you don't second guess).

    Also for airplanes. As it has been discussed, it's not an issue of interference for the plains electronics, but rather huge stress for the network.
    Could be handy to mount some of these at the airplanes ceiling and equip it with a moderately toned piezo buzzer to remind anyone who has forgotten to switch off their phone. Shouldn't get false positives from terminal either while on ground, as the planes are usually more than 30 meters from there.
    The piezo buzzer would be probably sufficiently collectively annoying to encourage any bonehead to shut off their phone too :)

    (Shameless plug. Check my sig. New release today)
  • It will not detect a off device. A bad guy who wants to sneak in and start calls from a secured facility can simply turn off his fone, put it inside a coke can and then turn it on when apropiate.
  • More useful to junior criminals would be an expensive cell phone detector that only detects triband models with cameras, avoiding the tedium of finding you've mugged someone for a cheap phone.

    I think a cheap detector for cell phones is meant.

    And now having exhausted the day's ration of pedantry, to work.

  • How is this news? People have been selling cheap decorative bands for mobile phones, pens and other items that light up moments before a cell phone lights up.

    It's quite popular with the ladies over here and they are onlyh about RM$5 - 20 each.

    So these kids put in 4 LEDs instead of 1. Big deal.

  • Another proof of the superiority of CDMA over GSM for cheating :-). GSM uses a modulation scheme that is easy to detect with relatively simple electronics. CDMA phones output a signal that looks like wideband white noise at a very low power level. It's difficult to detect or jam.
  •'s called an unshielded speaker. Whenever any data is being transmitted by my phone, my speakers go nuts.

    Based on the distance from the speaker (or wire), I can tell how far away the phone is.

    On a serious note, the device is simple. The complex part comes in if they can triangulate the actual 2D or even 3D position of the phone, not just the radial distance. Then I'll be impressed...
  • My crappy speakers make a noise 2 seconds before my phone or my neighbor's cell phone starts ringing.
  • In the classroom (Score:2, Interesting)

    by enigmax01 ( 785835 )
    I can see this technology being implimented in the classroom where most mobile devices are prohibited, especially in high-schools. Professors get sooo agitated when someones cell goes off... This may help them in detecting if students are messaging during class... or even worse... a test.
  • A hundred dollars or so.
    Evenif it was illegal.

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