Cellular service providers use two methods to determine the location of a cell phone through cell towers: digital pinging and analog triangulation. A digital ping requests latitude and longitude data from the cell phone, while analog triangulation uses the tower antennae sector and response lag time to estimate a location.
Digital pinging of a cell phone transmits a GPS data request from the transmitter built into the phone and pinpoints the location of the cell phone within 50 to 100 feet. This transmitter activates automatically when a user initiates a 911 emergency call. Cellular service providers activate the transmitter at the request of law enforcement personnel when the cell phone owner is the subject of an ongoing criminal investigation or is the victim of kidnapping.
The use of triangulation to locate a cell phone requires the simultaneous use of three cell towers. Cell towers use three separate antennae sectors to provide coverage to the area around them. Each sector covers 120 degrees of the service area. By identifying the correct sector providing service to the cell phone, the cellular provider identifies a general area of the cell phone. The response lag time provides the cell phone's distance from each cell tower and pinpoints the intersection of the service areas, which reduces the potential cell phone location to approximately a 3/4 square-mile area.