I went and saw the movie “16 Blocks” yesterday… it’s got Bruce Willis in it and was actually a pretty good movie… but I digress.
There’s a scene where Bruce is running through the streets of Manhattan trying to avoid being captured by the NYPD. Of course he doesn’t realize it but his Motorola i530 cell phone is being tracked, presumably by GPS. (I recognized the phone because I happen to have the same brand and model).
Now I know this is a movie and not reality, but assuming your phone has GPS built-in can the phone company (or law enforcement) track your whereabouts without you knowing it? I thought you needed 3 points in order to be triangulated. :dubious:
Assuming #1 is true they show a computer screen with street names and are able to pinpoint him to a particular position on a particular street. Is that possible using current GPS technology?
It would depend on the software in the phone. I used to have a Motorola phone with GPS that claimed that it only transmitted GPS location information to the cell phone company’s base station when the user dialed 911.
Your phone checks every few minutes for the best signal. It broadcasts and may get replies from 5 different towers and selects the one with the best signal strength. Depending on how directional the antennas on the tower are someone with the cell phone company could probably keep pretty good tabs on your movements WITHOUT GPS.
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2) Assuming #1 is true they show a computer screen with street names and are able to pinpoint him to a particular position on a particular street. Is that possible using current GPS technology?
Thanks for setting me straight on this…
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The millitary has been dropping GPS guided bombs for quite a while, IIRC within 5-10 meters of a specified point, that close enough for you.
Granted it could be wandering into GD territiory but as criminals become more information technology dependent, you will see more technology developed to track, circumvent or intercept that information.
It’s not clear whether a cell phone transmits GPS data when it does not have a call in progress. The technology is certainly available but I would be surprised if it did this in reality, because of the energy drain on the phone to transmit information that isn’t useful to anyone anyway. As mentioned in an earlier post I think they broadcast GPS data only when making a 911 call.
as a matter of fact, down here in chile, you can contract a service with your cel operator, where you call a certain service number, and you will talk to a live person to ask for the next pharmacy / metro-station / etc… BASED ON YOUR ACTUAL LOCATION.
Its done by triangularing the “my cel is negotiating with 5 different antennas” signal - and is only an approximation - I heard something like a radius of 100meters or so …
Multi-sector antennas are common in cellular systems. That would provide a general direction. Distance can be determined by measuring the propagation delay between the base station and the handset.
There are several facts being flung around here, not all of which really pertain to the OP.
On cell phones without GPS capability the location of the phone can be pinpointed with reasonable accuracy by triangulating the signal between several towers. Accuracy will depend on the number of nearby towers and various other factors. This is not as precise as GPS.
A GPS equipped phone will always know internally where it is located with very precise accuracy, probably within a few feet.
The crux of the matter is, does the phone transmit its location constantly to the phone company? I don’t think so.
My phone (a Samsung) has a menu option for GPS settings with the choices: Location On or 911 Only. If I set it to 911 Only, I’m pretty sure that my location is transmitted only when I am making a 911 call. I’m also pretty sure that the “Location On” setting means that the location is transmitted any time a call is in progress. I don’t think that the location is transmitted when I’m not talking, but I could be wrong.
Does anyone who works in the cell phone industry know how this actually works?
It is not triangulation. GPS and using the location of cell phone towers gets location from knowing the distance from the tower or satellite not knowing the direction. It is somewhat of a nitpick but I think it is important.
Not really the cell phone only knows the location if it is told to discover it. Either by the user or by command from the network.
I don’t think that phones will transmit this all the time either. One of the main selling points of one phone over the other is the stand by time. If the phone has to determine it’s location every few minutes or seconds for the OP scenario the standby time goes to hell because the RF is on many times longer than just checking with the network for calls.
It’s technically called trilateration, I think, but “triangulation” is used so often with GPS and cell phones that people seem to have grown used to it.
You do have 3 points – satellites hovering high above you. Your GPS unit receives time signals broadcast from three or more satellites. It then compares the time delay from each satellite to its internal clock and calculates the distance to each satellite. With three or more satellites of known position, the GPS unit can then calculate your own position.
Then, if your GPS unit also happens to be your cell phone, it can choose to send that location information to law enforcement agencies. Whether it actually DOES so is anyone’s guess, but it’d be a legal decision and not a technical problem.
It’s not that they’re tracking the location of his cell phone per se, it’s that his cell phone is tracking its own location and then sending that data to them. Subtle but important difference.
And yeah, even without GPS, an approximate location can be obtained with cell towers using the same principles.
Easily. That’s how car navigation systems do their jobs.
Worse than that, there are companies working on GPS phone localized spam. That’s where your cell phone suddenly pops up “You’re only about 10 steps away from Fred’s Used Cars, where today they are offering no-down-payment deals to Verizon users like you, Mr. Smith. Our salesman will be waiting by the door to show you how we can replace your 5-year-old Chevy with one of our cars.”
Just walking down a commercial street might someday get you bombarded by offers. And they can identify you specifically from your cellphone number, track that to public records like your automobile registration, and have customized ‘offers’ ready for you.
Frankly, that seems to me to be yet another reason to avoid having a cell phone.
[The Casinos in Atlantic City used to do a low-tech version of this. They hired people to sit alongside the highways and record the license plate numbers of people driving into the city, looked those up to get names, checked the hotels for those names, and by the next morning, had a coupon in your front-desk mailbox offering you deals if you visited their casino in town.]
And regarding the OP, I’ve heard that “running through the streets of Manhattan” you won’t get very good GPS coverage, because the tall buildings make it hard to get a clear signal from multiple satellites. Any GPS users in Manhattan who can report on this?
(Cell phone tower locations are designed to deal with this, and you only need to link to one of them.)
GPS units use 4 sat’s not 3, if only 3 can be locked onto then the center of the earth is used for the 4th (the unit assumes a altitude), and you get 2D navigation. The 4th ‘point’ is used to limit the amount of error that would happen with only 3.
Also yes manhattan’s high buildings usually knock out GPS signals, and also cause them to ‘reflect’ off buildings, creating huge errors. Regular consumer grade GPS would be next to useless there, now perhaps (I suspect) there are military ones that can do much better.
Some have suggested mapping a city’s WiFi points, both public and private, as a guidence system to augment gps car navagation, since they don’t move around much.
There are new GPS chipsets that are 10-20 dB more sensitive than a common GPS receiver. These will enable GPS reception in many areas that are currently thought to be unusable, such as in cities and inside buildings.
In Britain one can sign up for a service where the location of a cell phone is tracked and displayed to anyone who pays for the service. Note that one doesn’t have to own the cell phone being tracked. You can sign up to track the phone of anyone. Now the company selling this service takes steps to determine whether the individual carrying the phone wants to be tracked-but those steps are easily (according to the BBC who ran a story on this recently) circumvented. So yes, Bruce is toast.
As I understand it, Unless the phone is reprogramed, the GPS tracking is only used when calling 911. Of course you have no control over when your phone is reprogrammed-the software is uploaded whenever the phone company has a patch to install.
Every phone I have had in the last 2 years (which is several, I have a bad habit of loosing/breaking phones) has come with gps that can be set to either 911 only or “on” presumably meaning that it is transmitting all the time.
Is Verizon playing fast and loose with their terminology or what?