I mostly understand how cell phones work. What I don't get is how my cell phone (or more precisely, my cell phone provider) knows where I am when I'm far from home--"roaming," in cell-phone parlance. Is someone or something continually tracking my whereabouts, no matter where I am on the face of the earth? This thought manages to be comforting and scary at the same time. --Tony C., via the Internet
Of course they're keeping track of your whereabouts, knucklehead. Otherwise your cell phone wouldn't work. What's even scarier (or more comforting, depending on your mood) is that soon they'll be able to track you to within a radius of 50 meters. Will Big Brother be watching you? Maybe. Of more immediate concern is the fact that your friendly local retailers may be watching you too.
First the technical stuff. The genius of cell phones is that they enable multiple users to share the same radio frequency--you realize cell phones are basically radios, right?--by dividing the world, or at least the affluent urbanized part of it, into a hexagonal array of cells, each of which has an antenna at the center. Your cell phone communicates with the antenna at such low power that another antenna a couple cells away can use the same frequency for a different call with no risk of interference. (For details, including helpful illustrations, see www.howstuffworks.com and look up "cell phone.")
How does your cell phone provider keep track of where you are? When you switch on your phone, it uses a control frequency to tell nearby cellular antennas who you are and what your cellular provider is. If you're within your local calling area, your location and the fact that you're available for calls are stored in your provider's central database. If a call comes in for you, your provider looks you up, sees your phone is switched on, and routes the call to you via the closest antenna.
Things are only slightly trickier when you're roaming. When you switch on your phone and the cellular system in the area learns that you're an out-of-towner, it immediately notifies your cellular provider via a control circuit. (All of this takes just a second or two.) If a call comes in, your provider looks you up in the database as before, sees you're in a remote provider's service area, and routes the call there.
Now for the interesting part. Cell phones have long been used for communication during emergencies. Of 150 million calls to 911 last year, 45 million involved cell phones. Hardwired 911 technology automatically tells the emergency dispatchers where you're located so help can be on its way immediately. But with cell-phone 911 calls, the dispatchers know only that you're somewhere in the several square miles covered by a cell. The Federal Communications Commission has mandated that cellular systems figure out a way to tell 911 services the exact location of a caller. One popular approach: a tiny global positioning system antenna built into the phone. The GPS antenna picks up signals beamed out by GPS satellites that make it possible to determine your latitude and longitude. When you call 911, the cellular system automatically transmits your location too--or it will when the whole thing starts working. The FCC pushed back the starting date because the cell-phone industry hadn't gotten its act together on the technology. The new deadline for substantial completion is December 31, 2005.
E (for enhanced) 911 capability has lots of pluses. Apart from helping emergency dispatchers, it'll support some useful commercial services. Say you're driving in an unfamiliar town and you get lost. No prob--push a button and your cell phone sends your location to a navigational service that tells you which way to go. Similarly, you'll be able to request directions to shops and services in the vicinity.
On the other hand, do you always want the world to know exactly where you are? If you were a crook on the lam, using a cell phone would be tantamount to phoning in your coordinates. Most of us don't have anybody tailing us, but check out this scenario: you're walking past the grocery store when it detects that you're close by and sends you a message about today's sale on bananas. Excited? Creeped out and irritated is more like it, particularly since you're paying to receive the call. But the technology is ready to go. (Another concern: that unknown parties will track your movements over time, to God knows what nefarious end.) Sure, maybe there will be some way to opt out of things like this. But there's a good chance we'll wind up with cell phones and wireless handhelds and so on that combine the most delightful parts of spam and telemarketing. How come they never told us about this? "Kirk to Enterprise. Beam me up, Scotty." "In a second, Captain. I've got to scroll through the Viagra ads first."
Art accompanying story in printed newspaper (not available in this archive): illustration/Slug Signorino.