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      Cell phone technology used in search for missing teen

      No new developments Monday, in the search for a missing teenager from upstate New York. Searchers have focused on an area near the North Santee River, because that's where her cell phone last gave out a signal.

      17-year-old Brittanee Drexel from Rochester, NY was last seen Saturday, April 25th leaving the Blue Water Resort in Myrtle Beach.

      Investigators say her cell phone gave a signal to a cell tower in southern Georgetown County the night she went missing.

      The search has recently focused on the area along Highway 17 around the Santee River on the Charleston - Georgetown county line.

      Crews scoured the area this weekend, but came up short.

      A search that originates with a cell phone signal isn't always successful, but at least it gives searchers a starting point.

      Whether or not you're using it to make a call, whenever your cell phone is turned on, it's constantly sending a signal to towers near its location.

      If police know a missing person's cell phone number, they can have the phone company track down which tower most recently received a signal from that number.

      "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.

      Still, it's better than nothing. Graham says about the only thing that could have helped police narrow their search would have been more towers in that area.

      The process of calculating a cell phone location, is called "time difference of arrival."

      Anyone with information about Brittanee Drexel is asked to call the Myrtle Beach tipline at 843-918-1963.