GPS Monitoring

How It Works

GPS stands for Global Positioning System. GPS was developed by the U.S. Department of Defense as a precise navigation system for military applications, but has since been opened up to the public.

Twenty-four GPS satellites orbit the earth, constantly emitting radio signals. The satellites are positioned in space so that at least four are visible from any point on earth, at any time. These satellites are the foundation of GPS. Because these GPS satellites constantly "rain" signals down on the earth, anyone with a "bucket" or GPS receiver can "catch" them. Three people could have GPS tracking devices or three billion. It makes no difference.

A GPS receiver needs to "know" where the satellites actually are in order to calculate the receiver's location. This isn't particularly difficult because the satellites travel in very high and predictable orbits. The GPS receiver simply stores information regarding the satellites' position at any given time. Things like the pull of the moon and the sun do change the satellites' orbit very slightly but the Department of Defense constantly monitors their exact positions and transmits any adjustments to all GPS receivers as part of the satellites' signals.

When a GPS receiver locates and "catches" GPS signals, it measures how far away it is from each of at least four separate satellites. By calculating several locations over time, the GPS receiver can also compute speed and direction of travel.