As scary as it may be, the US Department of Defense has been using satellite technology to track the location of targets anywhere on Earth with pinpoint accuracy for the last thirty years. GPS, or Global Positioning System technology, lets GPS portable receivers pick up transmissions from four of the twenty-four tracking satellites.

By interpolating the data from the four satellites, GPS portable receivers are able to get a very clear picture of their own longitude and latitude, as well as the correct time. To be able to function properly, however, the GPS portable receiver must be positioned where it the satellite transmissions will not be blocked.

Sometimes a difference of a few feet can mean the difference between a clear signal to the GPS portable receiver, and a weak or blocked one. The GPS portable receivers are often incapable of receiving signals if they are being used near tall buildings or under heavy canopies of vegetation. The GPS portable receivers can be used indoors, but only with the aid of an external antenna.

Commercial GPS portable devices are now available in an amazing variety of applications besides stand alone receivers. They are incorporated into PDAs, wristwatches, and cell phones. And of course, there are portable GPS receivers for automobiles, motorcycles, and boats.

Features And Prices Of GPS Devices

One great appeal of many portable GPPS devices is their multi-functionality. A wristwatch with GPS capability, for example, is a great tool for those who enjoy outdoor pursuits like hiking, fishing, and camping; it eliminates the need for inconvenient maps. Having a GPS portable device in your PDA will be a great way to help you find your way around strange cities or find alternate routes when traffic is moving against you. For more info see http://www.gpssystemsreview.com/Articles/GPS_Tracking_System.php on GPS Tracking System.

The Garmin handheld GPSMAP 60CSx uses the state-of-the-art SiRFstar III chip to give it a nearly instant link--usually less than thirty seconds--to satellite transmissions even under heavy vegetation or in canyons. It is ideal for back country mapping and also has optional software to provide turn by turn directions and automatic routing.Listing for $536. it can be found on the Internet for $350.

The Garmin iQue 3600 PDA with GPS capabability, first introduced in 2003 with a sticker price of $589 is now advertised on the Internet for as low as $339.

Finally, the Garmin GPS Forerunner watch for runners, although they are far from elegant, is a waterproof training devise with technology which enable it to pick up satellite transmissions even among tall buildings or under heavy vegetation. These GPS watches can track distance and time and run about $240.