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
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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.”)
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.
Art accompanying story in printed newspaper (not available in this archive): illustration/Slug Signorino.
