The Facts

• GPS systems work by connecting your cell phone to orbiting geosynchronous satellites; "geosynchronous" means that they are moving at a speed which keeps them in the same location relative to the ground, matching the speed of the Earth's rotation. When your cell phone is in range of two GPS satellites, your location can be triangulated mathematically (the three points of the triangle are your cell phone and the two satellites). This location information is always available, by law, to emergency services when you place a 911 call, and is therefore available to your carrier as well. The best way to avoid having your location tracked is to turn off your cell phone.
  
  

Significance

• Location-aware services are now being offered, such as Google Latitude, which allows your location to be broadcast to your friends and contacts. This service is fully controllable by the user, who can modify his preferences to protect his privacy. Your GPS signal is always available to your network when the GPS is active---which can save minutes on emergency response times when 911 is called, and therefore save lives. (Phones without GPS can have their location determined less precisely for emergency purposes, by using triangulation from the cell network towers.)
  
  

Types

• Software services are either third-party applications or web sites (such as Google Latitude), or are part of your cell phone's operating system. Check your manual, or call your cellular provider, to determine if location services are automatically turned on in your phone. If location services are provided by network software, you will need to ask your carrier if you want your privacy protected more than the default settings provide.
  
  

Geography

• GPS relies on satellite technology and, theoretically, has a global reach, but it cannot penetrate most indoor or underground locations. GPS accuracy improves when you are in range of more than two GPS satellites.
  
  

Misconceptions

• Several web sites purport to allow anyone to trace any cell phone by typing their phone numbers into the site. These sites are hoaxes; while this data may be available via the methods listed above, none of these location tracking databases are publicly available.