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."

Comments

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.

Re:Neat, Now if only

[sr180]

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

[Osty]

... 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

[Albanach]

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.

Re:Neat, Now if only

[__aafkqj3628]

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.

Re:Neat, Now if only

[tzanger]

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.

Re:Neat, Now if only

[tomhudson]

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 p.It might be annoying if you were sitting right next to them, but not to the people a couple of seats away.

Re:Neat, Now if only

[Cpt_Kirks]

What about children, I know mine can be quite distracting.

That's why cars have trunks.

Re:Neat, Now if only

[BroccoliGod]

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 anti-fascists."

-BroccoliGod

Cheap Cell Phone detector?

[Flerg]

Why would you want to detect cheap cell phones?

Re:Cheap Cell Phone detector?

[Gordonjcp]

To save time when you're mugging people for their phone.

Already have one

[shird]

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.

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!

Re:Already have one

[Anonymous Coward]

How many dicks is that?

a lot.

Re:Tracking down specific people

[novalogic]

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 crowded the area is.

just dosn't seem like a good method based on the way it works.

Finally!

[WegianWarrior]

...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.

Got it already

[darnok]

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 ...?

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).

Re:This is news?

[tfb]

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 planes or in hospitals (both places where there is critically important small-signal electronics), in exams (no electronics, but pervasive cheating by text message), and in many other places. For those environments you want something which will detect a phone at significant range, and you *can't* assume that you can hear someone or the phone ringing: someone trying to cheat in an exam won't have the phone set to ring, and won't be talking into it.

Of course, you can get detectors already, but they're significantly expensive - hundreds of pounds. And you need plenty of them, too. Think about an exam: one for the room itself, one for each toilet, and probably at least one more for the corridors between the room and toilets. 4 or 5, minimum, or several thousand pounds. How many exam rooms does a school use at once? Maybe 5? So they might need 15-20 of these things. Not a small amount of money for a school. Similar things are true for hospitals and so on.

Reducing the cost by a factor of 10 or more, as these people have done, is a *major* advance. So yes, this is news.

Mobile detector pen

[worf_mo]

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).

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.

Its easy

[FraggedSquid]

Just listen for somebody shouting "I'M ON THE TRAIN!". As if we didn't know already.

Coming soon to a movie theater near you

[Lord Kano]

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.

[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

Simple explanation on directionfinding by radio

[WegianWarrior]

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.

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.

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.

I remember

[lachlan76]

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.

Re:30 metres?

[nkh]

If you want an exact conversion, 30 metres is equal to 3000 centimetres ;)

Technical article?

[europrobe]

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.

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 :-)

Re:It Figures

[builderbob_nz]

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 Aussie, but I can't resist) woo-hoo another Kiwi first!

Ears

[tiredwired]

Ears are so cheap I got two of them. I can detect cell phones quite well.

Re:Detect this

[Alranor]

Last I checked this was still the "land of the free".

Just out of curiousity, how many years has it been since you checked that?

Isn't that why the phone rings?

[TheOtherAgentM]

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.

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

Alternate suggestion

[TheCyko1]

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

How about.. no.

Re:Similar one in my car

[OneSeven]

...........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!!)

RF Interference sensitive areas.

[Fizzl]

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)

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.

Jammers violate FCC regulations

[KenSeymour]

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 one of the most important when it comes to selling cell-phone jamming equipment. One distributor (who wished to remain anonymous) told me they've exported approximately 300 jammers to the United States this year, more than to any other country. The exporter claims that buyers include restaurants, schools (including some universities, which have installed the technology to stop students from wirelessly diddling away on their phones during lectures), and personal users.