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Let's face it; we're in love with the idea of secret location trackers. In The Da Vinci Code, the bad guys slap a location-tracking button onto Tom Hanks's clothing. In The Matrix, a location-tracking robot crawls into Keanu Reeves's abdomen. Many parents may have dreamed of equipping their kids with such tracking devices, to find out instantly where they are at all times. Now, there is one sci-fi gadget that's no longer fi, thanks to advanced sci—satellite-based tracking using Global Positioning System (GPS) technology. At least five companies have built GPS tracking into cell phones. Advocates say such parental controls help keep kids safe, but it's worth pondering the moral implications. What these companies are selling parents is, in effect, a spying tool, and a chance to play Big Brother, or rather, Big Momma or Big Daddy.

—David Pogue