Cell phones can be tracked for a number of reasons. Users can track the location of their cell phones to establish present location and find routes to a particular destination. Emergency services can also track the location of a cell phone to better assist people in need.
Cell phone tracking starts with internal data in the cell phone that identifies the subscriber to the cellular network. In phones using the Global System for Mobile communications (GSM), the most popular standard for mobile phone service globally, subscriber data is contained in a card called a Subscriber Identity Module (SIM). Code Division Multiple Access (CDMA) is the most common mobile phone standard in the United States. In CDMA phones, subscriber information is programmed into the phone itself.
Cellular Tower Tracking
The most basic method of cellular phone tracking is via cellular tower triangulation. Cell tower triangulation measures the signal strength from nearby towers and calculates the approximate position of the cell phone. Accuracy of this method of tracking ranges from 200 to 1000 miles.
Some cellular phones contain receivers for Global Positioning System (GPS) satellites. If this receiver is turned on, the cell phone can be tracked to between three and 10 miles of its actual location. Most handset models have privacy settings that can be switched on and off to prevent this location from being sent to the network.
Hybrid Wi-Fi Network Tracking
A relatively new way of tracking cellular phones relies on the prevalence of Wi-Fi networks. Hybrid tracking systems are useful in deep urban areas where a clear view of the sky, required by GPS, is not available. Hybrid systems use a combination of cellular tower triangulation and sensing nearby known Wi-Fi networks to establish a much more accurate position than through tower triangulation alone. Some hybrid systems also use the few GPS satellites that can be acquired in heavily built up areas.
Through various types of tracking systems, cellular phone locations can be pinpointed to between three and 1,000 miles of their actual location.