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Cheap Cell-Phone Detector

Posted by timothy on Wed Jul 21, 2004 02:58 AM
from the and-tim-gets-10%-for-fairness dept.
Security Communications Wireless Networking Hardware
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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  • Neat, Now if only (Score:5, Interesting)

    by novalogic (697144) <aramovaNO@SPAMgmail.com> on Wednesday July 21 2004, @03:00AM (#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.

    • Re:Neat, Now if only (Score:5, Funny)

      by sr180 (700526) on Wednesday July 21 2004, @03:01AM (#9757518) Journal
      Great, so they look at their phone to work out why it dropped out right as they swerve their vehicle into you..

        • Re:Neat, Now if only (Score:5, Insightful)

          by tzanger (1575) <akohlsmith-sd@mixd[ ].ca ['own' in gap]> on Wednesday July 21 2004, @06:29AM (#9758168) Homepage

          The only thing that stops me is that it would jam medical pagers for doctors and emergency service reserves on duty..

          That, and I'd personally beat you senseless for determining that you have any say whatsoever over my use of a cell phone on a train, bus or any other form of public transit. I am perfectly capable of using my cellphone properly; your use of vigilante justice would earn you some in return.

          • The only thing that stops me is that it would jam medical pagers for doctors and emergency service reserves on duty..

            That, and I'd personally beat you senseless for determining that you have any say whatsoever over my use of a cell phone on a train, bus or any other form of public transit. I am perfectly capable of using my cellphone properly; your use of vigilante justice would earn you some in return.

            To paraphrase Ennio Flaiano: "On Slashdot there are two kinds of cell phone fascists: fascists and

              • An excerpt from an article in slate:

                In the United States, actively jamming a cell-phone signal is illegal. The FCC, which is the government agency in charge of regulating the airwaves, has established severe penalties for doing so. If you're caught at your local restaurant with the SH066PL2A/B, it's possible you could face an $11,000 fine and a one-year jail term. Possible, but apparently highly unlikely. It seems that the FCC has never charged anyone with this crime, even though the American market is o

        • I'd love to be able to press a button and jam their conversation, especially as most are conducted at about

          40db.

          Bzzzt! Wrong answer :-) A normal conversation is 60 decibels. 40 decibels is 1/100 of that. http://science.howstuffworks.com/question124.htm [howstuffworks.com] p.It might be annoying if you were sitting right next to them, but not to the people a couple of seats away.

    • ... 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?

    • Re:Neat, Now if only (Score:5, Insightful)

      by Albanach (527650) on Wednesday July 21 2004, @05:02AM (#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.

    • 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 [dyndns.org])

      Also, this device these kids are touting is nothing new. A google search will reveal various circuits schematics for cell phone detectors.

  • Cheap Cell Phone detector? (Score:5, Funny)

    by Flerg (152285) on Wednesday July 21 2004, @03:00AM (#9757511)
    Why would you want to detect cheap cell phones?

  • Already have one (Score:5, Informative)

    by shird (566377) on Wednesday July 21 2004, @03:04AM (#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:

    dicky-dick-dicky-dick-dicky-diiiiiick

    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.
    • 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?

      • *ANY* GSM will do that to poorly insulated speakers, especially if there happens to be a bit of cable with the magic wrong length just before the audio amplifier. f'r instance, I had to cut the cables of the speaker for a radio alarm clock I have in my bedroom (I use it only to project the time on the ceiling, I'm using a proper audio device for waking up purposes). The thing was detecting my cell phone 7 or 10 meters away (which pretty much means anywhere in the flat, plus the neighbour's phone at times).

  • Finally! (Score:5, Funny)

    by WegianWarrior (649800) on Wednesday July 21 2004, @03:05AM (#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?

      • Simple explanation on directionfinding by radio (Score:5, Informative)

        by WegianWarrior (649800) on Wednesday July 21 2004, @03:22AM (#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.

        • Heck, I was just thinking Geometry. I was picturing standalone antennae. The way you described it makes sense. The third point is the user. Thanks for the other info tho. Gives me a few ideas.
        • dont even need to be that difficult.

          two antennas vertical, standard whips. about 2 feet apart, although 1 foot apart works great.

          switch between the antennas at about a 500hz-1Khz speed, not hard at all with a timer/clock chip and a couple of mosfets.

          listen to the transmission. you will hear the switching frequency... now rotate the antenna until the tone goes away. That is the direction (or 180 away from it) that the transmitter is in.

          but within 30 meters all RDF finders saturate and finding the transm

  • Got it already (Score:3, Funny)

    by darnok (650458) on Wednesday July 21 2004, @03:05AM (#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 ...?
      • It still only tells you when something is happening, and an (approximate) distance from the detector where it's occurring. How will this help to detect cheating during exams, where there are potentially 100s of students within a 30m radius? Sure, they'll know a phone is being used, but who's using it? Is the plan to stop the exam and have everyone turn out their pockets?

        I haven't taken exams for many years, but I know several people that rely on mobile phones for critical reasons (e.g. being in touch fo
  • 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 [army-technology.com] (this one isnt pocket sized) are already avaialable.

  • This is news? (Score:4, Interesting)

    by Captain_Chaos (103843) on Wednesday July 21 2004, @03:10AM (#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!

    • 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 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, @03:12AM (#9757557)
    Just listen for somebody shouting "I'M ON THE TRAIN!". As if we didn't know already.
  • 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.

    LK

  • The MPAA will be using technology like this soon. (Score:3, Interesting)

    by GrpA (691294) on Wednesday July 21 2004, @03:18AM (#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...

    GrpA
  • 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) <lachlan.gunn@int ... et minus math_go> on Wednesday July 21 2004, @03:39AM (#9757677)
    I've seen something similar to this before [wenzel.com]. 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) <daniel DOT perup AT swipnet DOT se> on Wednesday July 21 2004, @03:59AM (#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.

  • Ears (Score:4, Funny)

    by tiredwired (525324) on Wednesday July 21 2004, @04:01AM (#9757735)
    Ears are so cheap I got two of them. I can detect cell phones quite well.

  • Isn't that why the phone rings? (Score:3, Funny)

    by TheOtherAgentM (700696) on Wednesday July 21 2004, @04:11AM (#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.
  • 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...

    --Tomas
  • 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)
    • I would doubt that. First of all, you'd have to do an awful lot of needless "Ping'ing", and if the person knew there was a danger, simply turn the phone off.

      And ofcourse, you need to beable to send this kinda stuff, I've seen it reported that IM services keep limited logs of IP's that use that.

      Besides, if your gonna stalk someone, and be within 30 meters, AND have an active connection to Yahoo, you'd beable to use better ways to locate the person then a radio ping which may or may not work based on how cr
      • There are so-called "quiet" SMS that the police use for tracking cell phone users. These are SMS without text payload which "ping" the mobile phone without ever showing up on the display.
        Of course, their tracking method goes a bit different: they triangulate the distance from the towers. Since every cell phone tower consists of an array of antennas, you can simply measure on which antenna the signal is strongest for an approximate direction. Combined with the distance measurement (from signal strength), thi
    • I think that at least one use of them was mentioned in the article (but of course, who reads that, nowadays?) in that students use them on silent mode during exams. Schools aren't necessarily the richest institutions in the world either.

    • I wouldn't go to the extent as saying that Tait was the largest tech exporter from NZ (OK its a given for hardware, but what about software?) but I think that it's great that they are encouraging kids to be creative and have fun learning about new things (heck, they probably now know more about my own cell phone than I do).

      My hat comes of for Tait, and I challenge all those slashdotters in decision making positions to get the kids off the streets and get them involved.

      And finally (sorry all those in Aus

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