The Global Positioning System (GPS) is a navigation system based on a network of satellites. By using GPS, you can find your exact location at any time.
GPS satellites circle Earth twice a day and send radio signals with such information as their locations and time. A GPS receiver, such as a GPS unit or a GPS app on a mobile device, picks up the signal. The GPS receiver then calculates your location by using the information received from four or more GPS satellites.
Personal Locator Beacon
Personal locator beacons (PLBs) provide a distress and alerting system for use in a life-and-death situation. A PLB is a small transmitter that sends out a personalized emergency distress signal to a monitored satellite system. When you buy a PLB, you must register it with the National Oceanic and Atmospheric Administration (NOAA). PLBs are a highly effective and internationally recognized way to summon help.