GPS is a satellite-based navigation system consisting of 24 satellites placed into orbit by the U.S. Department of Defense. It was originally intended for military use but is now available for civilian use free of charge. GPS works globally under any weather conditions using satellites to calculate location via trilateration. Common GPS devices include those in cars, phones, and pet collars that receive location data from satellites. A GPS receiver receives radio signals from multiple satellites to calculate its precise position on Earth.