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Cheap Cell-Phone Detector

timothy posted about 10 years ago | from the and-tim-gets-10%-for-fairness dept.

Security 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."

cancel ×


first post (-1, Offtopic)

Anonymous Coward | about 10 years ago | (#9757507)


Fuck you gaynigger bastards!

oooby dooby fp (-1, Offtopic)

Anonymous Coward | about 10 years ago | (#9757508)

fp, baby

Re:oooby dooby fp (-1, Offtopic)

Anonymous Coward | about 10 years ago | (#9757520)


I got you good you fucker!

Re:oooby dooby fp (-1, Offtopic)

Anonymous Coward | about 10 years ago | (#9757550)

For some reason, all I can picture when you say "I got you good you fucker!" is Farva from Super Troopers.

Re:oooby dooby fp (-1, Offtopic)

Anonymous Coward | about 10 years ago | (#9757616)

That's exactly what I was referencing, actually.

Long live Rod Farva and Car Ramrod.

Neat, Now if only (5, Interesting)

novalogic (697144) | about 10 years ago | (#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 (4, Funny)

sr180 (700526) | about 10 years ago | (#9757518)

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 (0, Offtopic)

double_plus_ungod (678733) | about 10 years ago | (#9757736)

they can't swerve their vehicle if their boxen are infected with virii thus allowing the detection unit to transmit spam, even through the reverse firewall.

Re:Neat, Now if only (0)

Anonymous Coward | about 10 years ago | (#9757756)

virii and boxen eh?

The only phrase flamebait you forgot was 'begs the question'.

Re:Neat, Now if only (2, Insightful)

Osty (16825) | about 10 years ago | (#9757523)

... 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?

microwave faq (1)

mihal (753927) | about 10 years ago | (#9757687)

1st, to jam anything you need far more power then the target. 2st, since celular (1800 or 1900 MHz) wavelenth is about 15 cm, your antenna has to be as least 45 cm for so-so diffusion cone. otherwice, the mentioned power will spread everywhere and fry your brains (consider you have some) and it has to be a dish or phased array. 45 cm dish is not a good thing to aim with while driving.

Re:Neat, Now if only (1)

bruthasj (175228) | about 10 years ago | (#9757851)

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.

Cheap Cell Phone detector? (5, Funny)

Flerg (152285) | about 10 years ago | (#9757511)

Why would you want to detect cheap cell phones?

Re:Cheap Cell Phone detector? (1)

sotonboy (753502) | about 10 years ago | (#9757559)

A surprisingly accurate answer to this question is available online. Just click on the link to the article, and READ IT.

Re:Cheap Cell Phone detector? (1)

boogy nightmare (207669) | about 10 years ago | (#9757568)

Look at the parent post again and READ IT. :P

Re:Cheap Cell Phone detector? (0)

Anonymous Coward | about 10 years ago | (#9757613)

Look at the parent post again and READ IT. :P

Read? Come on now, you know thats asking alot of the average /. reader.

Re:Cheap Cell Phone detector? (0)

Anonymous Coward | about 10 years ago | (#9757667)

the title of the post is "Cheap Cell-Phone Dectector"...the parent comment is making fun of the detects cheap cell phones...its supposed to be funny :D

Re:Cheap Cell Phone detector? (0)

Anonymous Coward | about 10 years ago | (#9757681)

No silly, it's a "Cheap Cell" "Phone Detector". You know, a phone detector that runs on cheap AA cells.

Sheesh, *read* the durn thing.

Re:Cheap Cell Phone detector? (2, Funny)

Gordonjcp (186804) | about 10 years ago | (#9757840)

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

Tracking down specific people (0)

robolemon (575275) | about 10 years ago | (#9757515)

Seems to me like you could use this to trace someone down by text messaging them repeatedly and tracking them down. Coupled with using something like Yahoo! Mobile to send the messages, this seems like it could cause some definite privacy concerns.

Re:Tracking down specific people (3, Informative)

novalogic (697144) | about 10 years ago | (#9757526)

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.

Re:Tracking down specific people (1)

Pius II. (525191) | about 10 years ago | (#9757572)

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), this gives quite a nice accuracy (~100m). Of course, that would be of no use on large events, but it's enough to track, say, a software patent violator in the woods.

Note that here (in Germany) you officially need a judges permit to actually use this technique, but since these messages are basically invisible, their use without permit is to be strongly suspected. Here [] is an article (in German) dealing with this topic.

Re:Tracking down specific people (0)

Anonymous Coward | about 10 years ago | (#9757590)

if you have access to node information, the cell company already knows where you are in order to send messages to you.

signals are emitted every so often, in order to keep track of you as you move out of range and into the range of another cell (tower, not phone).

the idea of 'pinging' using sms, is daft, unless you had access to that phones engineering screen and also a list of the node addresses. either that or access to the cell network.

KISS people (1)

tod_miller (792541) | about 10 years ago | (#9757635)

Just dial their phone and follow the ring tone!

Brought to you by the tin hat brigade.

oh no, not another list! (0, Troll)

lanswitch (705539) | about 10 years ago | (#9757521)

as initiator I get 5% of gross profits

1. post cheap hack on slashdot.
2. ???
3. Profit!!!

Re:oh no, not another list! (1)

Caedar (635764) | about 10 years ago | (#9757538)

Oh no, not another overused joke!

Already have one (4, Informative)

shird (566377) | about 10 years ago | (#9757524)

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 (0)

Anonymous Coward | about 10 years ago | (#9757531)

What brand phone/service do you have?

Re:Already have one (1)

Chep (25806) | about 10 years ago | (#9757578)

*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).

Crappy old CRTs (or crappy obsolete VGA cables) will also give you some funky video too. El-cheapo car radios are also especially prone to this too.

Re:Already have one (2, Interesting)

jlanthripp (244362) | about 10 years ago | (#9757571)

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 (1)

Chep (25806) | about 10 years ago | (#9757634)

fuck Cingular, then. I have zero coverage problems with Orange or Vodafone. And Bouygues' extended coverage GSM+ is reported to rule.

Oh, wait.

Re:Already have one (1)

nkh (750837) | about 10 years ago | (#9757658)

The sound is more like a tu tu-lu, tu tu-lu but it was not my problem: I never had this kind of sound without a call. I would be freaked out if my cell phone was calling home like yours every 10 minutes. Of course it could be explained by your dead zones with the phone trying to amplify its signal, thus producing the magical music.

Re:Already have one (0)

Lord Kano (13027) | about 10 years ago | (#9757588)

And from under your desk eminates the sounds



Re:Already have one (1)

mge (120046) | about 10 years ago | (#9757631)

The GSM phones do this over our desk phones

Re:Already have one (1)

Artega VH (739847) | about 10 years ago | (#9757669)

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..

Re:Already have one (0)

Anonymous Coward | about 10 years ago | (#9757684)

Everytime a cellphone gets a call/text i get a:


i dont know what kind of people call you...but i never get phone calls about dicks.

Re:Already have one (1)

minus9 (106327) | about 10 years ago | (#9757697)


How many dicks is that?

Re:Already have one (2, Funny)

Anonymous Coward | about 10 years ago | (#9757715)

How many dicks is that?

a lot.

Not quite... (1)

Airw0lf (795770) | about 10 years ago | (#9757768)

It's not just everytime you get a call or text message. Sometimes I hear that sound even though I don't receive a call or a message. It might have something to do with the phone changing from one cell tower to another or something, or simply being polled by the cellular operator.

Finally! (5, Funny)

WegianWarrior (649800) | about 10 years ago | (#9757528)

...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.

Re:Finally! (1)

geminidomino (614729) | about 10 years ago | (#9757543)

How do you get 2 antennas 90 degrees apart? Wouldn't you need THREE points?

Simple explanation on directionfinding by radio (4, Informative)

WegianWarrior (649800) | about 10 years ago | (#9757602)

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 (1)

geminidomino (614729) | about 10 years ago | (#9757699)

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.

Re:Finally! (1)

Lord Kano (13027) | about 10 years ago | (#9757603)

Once I dropped my cellphone into a 2 foot snow drift. I had to keep calling it and sifting through the piles of snow in my driveway. That sucked ass.


Where do they hide them? (1)

tod_miller (792541) | about 10 years ago | (#9757648)

"Prisons are difficult places because they are quite large and cellphones are very small."

If they sold these devices with a pair of rubber gloves, they are onto a winner!

Re:Finally! (0, Troll)

antic (29198) | about 10 years ago | (#9757659)

"don't laught"? I admidt that I don't even know what laught is! Maybe I forgots?

Re:Finally! (1)

jigyasubalak (308473) | about 10 years ago | (#9757794)

Mobile can still be found by calling to it thru the land line...ok, ok...almost everyone has a landline and mobile. I'd appreciate this in a keychain more.

Got it already (3, Funny)

darnok (650458) | about 10 years ago | (#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 ...?

Re:Got it already (1)

supersandra (788539) | about 10 years ago | (#9757552)

Sure, you have a point of some kind. However, this device could much better be used to detect cell phone use when people have a reason to conceal it. As a student I know that plenty of cheating via text messages and camera phone images goes on, as do the authors of the article. It even mentions that they're going to try out the devices at the boys' university during exams.

RTF post/article, you silly person... :)

Re:Got it already (1)

darnok (650458) | about 10 years ago | (#9757579)

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 for health reasons, contact with kids on public transport, etc.) that would make them reluctant to give them up for the duration of a typical exam. How is this issue currently handled in academic environments?

Re:Got it already (1)

wisdom_brewing (557753) | about 10 years ago | (#9757720)

currently, in the uk at least, there is a zero tolerance on mobile phones during exams, you hand in the phone at the start of an exam, and collect it at the end, it is asked that you do not bring the phone at all into the examination rooms, and if youre found with one you instantly get 0 for the exam you are taking (as with all cheating) even if it is switched off... as ive already said, if you HAVE to have a mobile phone on you, you switch it off and hand it to the invigilator...

Re:Got it already (1)

trendyhendy (471691) | about 10 years ago | (#9757796)

As someone who goes to said University (Uni of Canterbury) I can say that cellphones are allowed in an exam, but you must turn them off and leave them in your bag at the front of the room. Though that doesn't mean that everyone remembers to do this; the result is some LOUD polyphonic ringtone going off in the middle of the exam.

Re:Got it already (1)

Airw0lf (795770) | about 10 years ago | (#9757801)

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 for health reasons, contact with kids on public transport, etc.) that would make them reluctant to give them up for the duration of a typical exam. How is this issue currently handled in academic environments I am currently at university, and for the last couple of years, there has been a massive "crackdown" on cellphones in exams. If a phone is found on you at any point in the exam you will be escorted out and have to face a disciplinary hearing - which will probably end up in you being expelled for cheating. This applies even if your phone is turned off. I'm fairly sure you'd even get in trouble for having a phone with no battery :) Our exam procedure requires that bags be placed at the front of the room. If you have a phone in there and it rings, the bag will be taken out, and the owner will have to go to the exam centre to claim it. Upon claiming the bag, "appropriate action" will be taken against you by the chief examiner. So in this environment, I do not see any room for ANY cellphone usage at all, no matter how good the reasons for it. This is my university, YMMV.

Re:Got it already (1)

sotonboy (753502) | about 10 years ago | (#9757585)

1>. Sending text message. No sound created.
2>. Phones are constantly talking to the nearest base station. Even when youre not actively talking down it, a signal is being emitted.
3>. Silent (ringer turned off) calls.

reliability (1, Interesting)

dncsky1530 (711564) | about 10 years ago | (#9757537)

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.

Re:reliability (1)

sotonboy (753502) | about 10 years ago | (#9757600)

I dont think theyre trying to detect phones in a congested area. But I may be wrong because I acutually read the article. Its for use in Exam halls etc.

And as I understand it it, its a DETECTOR, not a jammer. Again though, I got this be READING THE ARTICLE, so I may be wrong.
Just to save you going to the troube of reading it yourself, it points out that detectors are also available, but are prohibitively expensive, this is a cheap version.

It Figures (1)

tonyr60 (32153) | about 10 years ago | (#9757539)

Christchurch is the technology centre of New Zealand, and Tait is the largest technology exporter

Re:It Figures (2, Insightful)

builderbob_nz (728755) | about 10 years ago | (#9757731)

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!

Sorry for replying to my own post... (1)

builderbob_nz (728755) | about 10 years ago | (#9757761)

But I just thought that my comment about being a Kiwi first is probably going to start a huge thread about reading the artical and getting my facts straight. What I meant was that it is a first that it is so cheap $40 compared to $1000. And it is a design so simple that a child could make it (although I must admit that I would have to try an remember which way up you hold a circuit diagram before I atempt it).

Re:It Figures (0, Offtopic)

sammcj2000 (763751) | about 10 years ago | (#9757763)

yay go christchurch!!!!!!! im a Opawa / St.Martins man myself!

This is news? (3, Interesting)

Captain_Chaos (103843) | about 10 years ago | (#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).

Similar one in my car (1)

tanveer1979 (530624) | about 10 years ago | (#9757691)

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!

Re:This is news? (0)

Anonymous Coward | about 10 years ago | (#9757742)

In Europe? That's nothing. They're really abundant... in Japan!


Mobile detector pen (2, Insightful)

worf_mo (193770) | about 10 years ago | (#9757551)

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 (2, Interesting)

pbjones (315127) | about 10 years ago | (#9757556)

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

Re:your distance will be wrong (1)

J Isaksson (721660) | about 10 years ago | (#9757759)

True, but it's still very useful for triangulating the phone with multiple sensors.

Its easy (5, Funny)

FraggedSquid (737869) | about 10 years ago | (#9757557)

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

Isn't it Obvious Anyway? (0, Redundant)

mauthbaux (652274) | about 10 years ago | (#9757562)

In my personal experience (living on a college campus) It seems that people with cell phones are plenty willing to show them off and use them (nearly constantly).
So what then, is the practical use of such a device? From the description it sounds like it would only detect a phone as it is receiving or sending a message anyway. Someone sending a message would be obvious enough anyway. When recieving a message, they seem to make pointlessly loud and obnoxious noises already. Pardon the skepticism, but I can't see much practical use for such a device (other than the obvious geek factor).

Now if you could integrate something similar into handheld console games, that would be a little more interesting. Imagine not only being able to play play the games against others, but getting a signal when someone around you has the same game and is willing to play agaisnt you.

Just my uninformed two cents

Re:Isn't it Obvious Anyway? (3, Interesting)

stupid_is (716292) | about 10 years ago | (#9757614)

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.

Coming soon to a movie theater near you (2, Funny)

Lord Kano (13027) | about 10 years ago | (#9757580)

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.


Re:Coming soon to a movie theater near you (1)

ragnar (3268) | about 10 years ago | (#9757727)

I would hope the cinema operators would eject anyone who would be so insensitive as to do text messaging during a movie.

Re:Coming soon to a movie theater near you (1)

Lord Kano (13027) | about 10 years ago | (#9757740)

My phone has a "silent" option, how about yours?

As long as they're being quiet, I don't care what they're doing.


Re:Coming soon to a movie theater near you (1)

AtomicBomb (173897) | about 10 years ago | (#9757746)

Cell phone detector has already been around... Whether cinema, university, prison etc decide to use it is another matter... It is cool to see young students designing those thing. But, the product is around for a while and it is
not really that expensive (click the third photo, the price is about 150 UK pound, about $270). Already quite affordable for the institute who want to install them...

The industrial guy who is mentoring the students exaggerates the price of rival product a bit (he said it is at least 350 UK pound), and ignored some cost. For example, to support the secondary student, the local university/ govt dept may not be hesitated to pay some cash to buy a bare board. To make a customer product, you need to have a decent case. Just the plastic mould can be a few thousand dollars... And, a real company need to pay their engineers. We all know we are not that cheap. My guess is they have not lowered the unit cost revolutionally. It is more like hobbyist vs commercial product...

It sounds cool to catch the students who cheat in the exam... But, in practice, it won't work esp in university. (Prison is another story)... Say, you are running an exam in a big lecture hall. Can you make sure there is no valid user around. The univeristy visitor may have one, the gardener mowing the lawn outside may have one, the courier may have one. Every single outsider walks near the lecture hall will signal a false alarm....

Re:Coming soon to a movie theater near you (1)

AtomicBomb (173897) | about 10 years ago | (#9757755)

Oops the link does not show up in the last post.
Here is the link to the $270 cell phone detector []

The MPAA will be using technology like this soon. (2, Interesting)

GrpA (691294) | about 10 years ago | (#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...


Detect this (0, Flamebait)

flopsy mopsalon (635863) | about 10 years ago | (#9757621)

I wonder to what extent use of this detector constitutes unreasonable search and seizure.

I pay good money for wireless phone service and I do not need snoopers with "cell phone detectors" singling me out as a potential troublemaker just because I prefer to stay in touch with others by carrying my phone around.

Last I checked this was still the "land of the free". I hope the proliferation of cheap cell phone detectors does not trigger a rash of racial profiling type incidents.

Land of the Paranoid (1)

CavemanKiwi (559158) | about 10 years ago | (#9757701)

Unless the USA is way behind the time I would say the majority of people have cellphones hence it is similar to people choosing to pick on people with 2 hands. In terms of search and seizure laws I guess this gets a little trickier. My 1st reaction was well your cell is broadcasting so it would the same as telling people to not listen when you are shouting. However what if the equipment would be capable of listening to your conversation that would kind of be spying and I am not so keen on that idea. But is it really different to someone eavesdropping on your conversation in public. So torn. /back to work

Re:Detect this (5, Funny)

Alranor (472986) | about 10 years ago | (#9757747)

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?

wow... (0)

Anonymous Coward | about 10 years ago | (#9757753) got ISSUES dood. You took a giant flying leap from a kid's science project to RACIAL PROFILING. LOLOLOL! You're a nut. Stay away from me.

30 metres? (0, Redundant)

phalse phace (454635) | about 10 years ago | (#9757623)

For those who are wondering, 30 metres = ~ 98.43 feet.

1 feet = 0.3048 meters

Re:30 metres? (0)

Anonymous Coward | about 10 years ago | (#9757646)

Or, if you're really picky, 30 meters = 98.4251969 feet [] .

Re:30 metres? (2, Funny)

nkh (750837) | about 10 years ago | (#9757679)

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

In HK (1)

QnA (747851) | about 10 years ago | (#9757629)

In HK, one of the most cellphone popular place, some karaoke do have such facility. Once the detector received any signal from the cellphone, it will display a sign on on the screen and minimize the background sound automatically to avoid effecting the conversation of the phone owner.

If it's New Zealand (-1, Offtopic)

Anonymous Coward | about 10 years ago | (#9757668)

Shouldn't it be pronounced "sull phone dituctor"

They've all got chronic vowel problems down there...

Cell phone noise (2, Interesting)

Caltheos (573406) | about 10 years ago | (#9757671)

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 (2, Informative)

lachlan76 (770870) | about 10 years ago | (#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? (2, Insightful)

europrobe (167359) | about 10 years ago | (#9757728)

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? (2, Interesting)

numo (181335) | about 10 years ago | (#9757783)

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 :-)

Ears (4, Funny)

tiredwired (525324) | about 10 years ago | (#9757735)

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

You insensitive clod!!!! (1)

Airw0lf (795770) | about 10 years ago | (#9757777)

I'm DEAF, you insensitive clod!!!!!

Re:Ears (1)

ravydavygravy (230429) | about 10 years ago | (#9757845)

Ears are so cheap

Really - have you tried buying any recently?

I own the patent! (0)

spookyfluke (254600) | about 10 years ago | (#9757745)

Ha ha! Time to start sitting back and watch the money roll in! :>

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

TheOtherAgentM (700696) | about 10 years ago | (#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.

Creative kids... (1)

zxflash (773348) | about 10 years ago | (#9757776)

Now if they could only invent something so that when i'm using a cell the person on the other end of the call can actually hear me and not just static and noise... You won't need a fancy device to find me... I'll have one finger in my ear and be screaming profanity throughout the duration of the call... You'll hear me from way more than 30 meters away!

This looks like a long range version of the... (1)

alex_ware (783764) | about 10 years ago | (#9757798) phone holders that had flashing led's that sold for £1.99

t'rollkorE (-1, Offtopic)

Anonymous Coward | about 10 years ago | (#9757804)

In the sun. In The and abroad for many of us are

A number of reasons this device might be practical (3, Interesting)

SmoothTom (455688) | about 10 years ago | (#9757811)

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...


What use is a detector? (1)

Airw0lf (795770) | about 10 years ago | (#9757816)

A detector will tell you that a phone is being used in a restricted area, but it won't help you find it that easily - especially if there are several in a room. The easiest solution for something like an exam room is a cellphone jammer. In saying that, this will only remedy exchange of information via cellphone. It will not prevent people from using their phones as calculators or as notebooks. So if you want to ensure that there is absolutely no cheating in an exam where no calculators are allowed, I would suggest an EMP grenade :)

Alternate suggestion (2)

TheCyko1 (568452) | about 10 years ago | (#9757819)

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

How about.. no.

detects cheap cell phones? (1)

Dwedit (232252) | about 10 years ago | (#9757847)

Whoa! I completely misunderstood this based on the headline. I thought it would detect which cell phones were cheap.
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