Cheap Cell-Phone Detector

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."

Neat, Now if only

[novalogic]

... 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.

reliability

[dncsky1530]

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?

[Captain_Chaos]

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).

your distance will be wrong

[pbjones]

mobile power output varies and is controled by the phone, you can't derive distant by looking at power output.

Re:Already have one

[jlanthripp]

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 MPAA will be using technology like this soon.

[GrpA]

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

Re:Isn't it Obvious Anyway?

[stupid_is]

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.

Cell phone noise

[Caltheos]

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.

Re:Technical article?

[numo]

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 - the adaptation schemes work during the call, but not during the control messages. The effects on my loudspeakers seem to support this theory :-)

A number of reasons this device might be practical

[SmoothTom]

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

Re:Simple explanation on directionfinding by radio

[Lumpy]

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 transmitter becomes skill and cunning now.

Me? I now use a dopplar RDF I got for $150.00 from ramsey electronics. 4 antennas and a 16 led display point the way to the transmitter.

No broadcast = No detection

[RogL]

ANYTHING that works by broadcasting a signal can be detected. Cellphone, cordless phone, spark-ignition, even your PC's emissions. That's life; deal with it.

If you don't want "snoopers", don't broadcast. So there's a solution to your concerns: turn off your cellphone when you're not actively talking. Periodically check voicemail, preferably while in a crowded area, where "they" can't track you down.

In the classroom

[enigmax01]

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.

Re:Neat, Now if only

[Anonymous Coward]

. . . and I'd personally beat you senseless for . . .
another Internet Tough Guy.

I've got the US model from www.globalgadgetuk.com, and needless to say, I'll use it whenever I want in a movie theater, restaurant, or other appropriate location where I spend money on the entertainment/environment.

Some people need to have their decisions made for them. It appears as if you might be one of those types as well.

You must think that you are pretty important to threaten violence to protect your cell phone usage.

I'm sure that your mom won't panic when she can't get in touch with you every half hour.