Cell Phone Pings and Pinging

A cell phone played a critical role in helping searchers find and rescue the wife and children of CNet senior editor James Kim after they had been stranded in the snowy Oregon wilderness for nine days, even though they were well out of cell phone range. (As of this writing, Kim himself -- who left his family on Saturday to find help -- is still missing.)
CNet News.com explains just how in a story examining the cell phone's growing role as a crucial lifeline for many:
Mobile devices are in constant communication with the network, constantly letting cell towers know of their location. Mobile operators don't typically store this information. So authorities are usually able to get information based only on the most recent "ping," or device communication, with a cell tower.
But when someone is missing, even this small bit of information can prove useful in determining the approximate location of a device. If the mobile subscriber is still within cell phone range, authorities can track the general movement by following the towers the phone has contacted or pinged. And if the cell phone goes out of range or runs out of battery power, the mobile operator will have a record of the last ping before the cell phone either lost its signal or lost power.
This is how authorities were able to home in on the general area where the Kim family was found, according to a sheriff's department spokesman during a press conference on Monday. A cell phone tower operated by Edge Wireless, the local cellular provider in the region, received a signal from one of the family's cell phones at about 1:30 a.m. November 26 near Glendale, Ore. ...
Authorities said the cell phone signal indicated only that they had been within a 26-mile radius of Glendale, where the tower is located. But people at Edge Wireless took this information and mapped the area, providing an approximate location of the Kims' vehicle, the sheriff's department spokesman said. And using this information, authorities sent out rescue teams, which eventually located Kati Kim and her children.
The GPS chips embedded in newer cell phones, which can be pinged directly by carriers, should make it even easier to locate missing people