Cell phones are constantly sending out signals, or "pings," that are picked up by the nearest transmission tower. In the reverse direction, rescue and law enforcement authorities can determine the pinged cell phone user's actual physical location when they cross-compare the phone ping's distance from a number of different transmission towers.

Emergency Origins

The ability to isolate a cell phone user's whereabouts based on that person's cell phone ping pattern was originally developed for emergency response purposes. Theoretically, if an individual dialed 911 requesting assistance but could not provide their address, the pinging of that person's cell phone could help fill in the blanks.

However, the ping technique has morphed into a much more powerful and commonly used law enforcement tool. It is especially valuable when attempting to retrace the previous whereabouts of a prime criminal suspect. However, this archived information is only as good as a cell phone provider's tower logs, and there are conflicting opinions on just how exhaustively this information is kept.

Real-Time Tracking

In the wake of 9/11, the sweeping powers given to the U.S. government have empowered federal officials to routinely request information about an active subscriber from that person's cell phone service provider. In some cases, the presiding judges at these warrant request hearings have waved the need for the federal officials to show "probable cause."

Experts agree that the pinging of a cell phone is now almost as accurate a gauge of someone's physical location as a law enforcement agency issued ankle bracelet. The commercial applications of cell phone pinging are also almost endless, from advertising the ability to be notified when friends are nearby, to parents being able to digitally chaperone their children. Verizon for example used cell phone pinging to market a "geo-fence" concept, whereby parents could delimit physical street boundaries and then be notified when their teen child crossed past the limit.