found this article about the cell tower ping down in Georgetown.
Cell phone technology used in search for missing teen
http://www.carolinalive.com/news/news_story.aspx?id=295450
snip:
"It's not a very specific area, it's a very vague area. Those cell phone towers can go for miles and pick up a signal so we have a general area to start searching at least."
Every signal that a cell phone sends to a tower has a time stamp attached to it.
By calculating the amount of time in milliseconds that it takes for the signal to get from the cell phone to the tower, the phone company can calculate how close the cell phone is to the tower.
Keep in mind, the cell phone is sending a signal to many towers at the same time, and HTC engineer Ryan Graham says, for tracking purposes, the more towers the phone can communicate with, the better.
"Depending on how far away it is from tower A to tower B, it will triangulate that position of that phone, depending on how many sites. Obviously, the more sites it can communicate with, the better or tighter that triangulation can come," said Graham.
Unfortunately, there aren't many cell phone towers in remote, rural areas like the Santee River where police searched for Brittanee Drexel.
That means the searchers have a much bigger area to work with.
"It can be anywhere from right near the cell site, within a half a mile to 5,6,7 miles away, radius around the cell site," said Graham.
