GPS (Global Positioning System) uses 24 satellites travelling in 6 orbital paths around the Earth at a distance of 12,600 miles. These satellites transmit a low power signal The pattern of their orbit is calculated so that a GPS receiver on the earth’s surface is always ‘visible  to at least 4 of these satellites.From these 4 satellite transmissions your GPS Tracker can work out your location. This is the same system used by car sat nav systems