GPS phones can pinpoint a location and give directions

A cell phone is basically a sophisticated two-way radio. Towers and base stations, arranged into a network of cells, send and receive radio signals. Cell phones contain low-power transmitters that let them communicate with the nearest tower.

As you travel, you move from one cell to another, and the base stations monitor the strength of your phone's signal. As you move toward the edge of one cell, your signal strength diminishes. At the same time, the base station in the cell you are approaching notices the strength of your signal increasing. As you move from cell to cell, the towers transfer your signal from one to the next.

In remote locations, towers may be so far apart that they can't provide a consistent signal. Even when towers are plentiful, mountains and tall buildings can interrupt their signals. Sometimes people have a hard time getting clear signals inside buildings, especially in elevators.

Even without a GPS receiver, your cell phone can provide information about your location. A computer can determine your location based on measurements of your signal, such as:

• Its angle of approach to the cell towers
• How long it takes the signal to travel to multiple towers
• The strength of your signal when it reaches the towers
  

Nearly all new cell phones sold in America have some GPS receiving capability built in. Those that don't can connect to a server that uses techniques discussed in the last section to analyze their signals and determine their location. This allows the phones to transmit a person's location to a Public Safety Answering Point (PSAP) after dialing 911. But that's all a lot of phones can do with their GPS.

However, some phones have a complete GPS receiver located in the phone or can connect to one with wires or through a Bluetooth connection. These GPS-enabled phones can understand programming languages like Java and can provide turn-by-turn directions or information about nearby businesses and attractions. Others can work like a tracking device. To use any of these features, you must have:

• Location Tracking
• Turn-by-Turn Directions
• Outdoor Location Services