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

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: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.

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.

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: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

[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.

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.