> # Global Positioning System
> Watching Over You
> By November 2001,

> The Global Positioning System (GPS) consists of 24 Earth-orbiting satellites. These satellites allow any person who owns a GPS receiver to determine his or her precise longitude, latitude and altitude anywhere on the planet. For as little as $100, you can know exactly where you are and where you have been. For anyone who has ever been lost -- while hiking in the woods, boating in the ocean, driving in a unfamiliar city or flying a small airplane at night -- a GPS receiver is a miracle. When you use GPS receiver, you're never lost.

> How is this possible? In this edition of HowStuffWorks, we'll look at the details of how the GPS satellites and GPS receivers work together to pinpoint a location. You'll find that the GPS system is an amazing technological tour de force!

> You may want to start with How They Work to learn how the GPS satellites and your receiver work together -- it's an amazing system! If you've never used a GPS receiver before, try What They Can Do to learn about what GPS receivers can do for you. Features tells you about all of the features you find on GPS receivers so you know what you are talking about if you are looking to buy one. Just click on the different areas of the map to learn all about these amazing devices!

> The following map leads you to all of the available information!

> How Location Tracking Will Work
> by Kevin Bonsor
> How Location Tracking Will Work
> Watching Over You
> A New 911
> Attention Shoppers
> Lots More Information!

> Digital Angel will allow you to not only locate someone, but also check on that person's health. Such a system will especially assist those trying keeping track of patients or elderly parents. Digital Angel combines wireless radio signals, GPS satellites and a ground-based data center to continuously track someone's location. Subscribers to the service will be able to log on from any Internet-connected device to check on a loved one.

> Digital Angel uses GPS satellites and an AT&T wireless network to track people wearing a BioSensor watch and GPS-equipped pager device.

> Here are the various components that make up the Digital Angel system:

> - Biosensor - Embedded in a wristwatch, this biosensor touches the skin and reads a person's vital signs, including temperature and pulse. A special algorithm allows the system to determine if the person has suddenly fallen down, a feature useful for some at-risk patients.

> Photo courtesy Digital Angel

> A person would have to wear this special watch and pager in order to be tracked by the Digital Angel network.

> - Pager device - Data from the biosensor is sent wirelessly to a pager device that has a GPS receiver and a cellular packet module or transceiver, which enables it to upload this information to a satellite. A microprocessor in the pager organizes the data flow from the GPS receiver and transceiver. Both the biosensor watch and the pager device will come with a rechargeable battery.
> - GPS satellites - Digital Angel uses these satellites and a remote monitoring station to continually ping (bounce radio signals to) the person's pager device. Radio signals from the satellite get a fix on a position, and the satellite then transmits a longitude and latitude to a GPS receiver.
> - AT&T wireless network - Once a person has been located, their information can be sent through cellular data packets to a wireless network. The data is sent over a frequency range of 800 to 900 MHz.
> - Delivery system - While AT&T provides the transmission of signals, Digital Angel provides the hosted data center. There are two of these centers in the United States, one in New York and one in Maryland. Proprietary software allows subscriber devices to interface with the data center. Users can log on and get information, along with a map of a person's location.

> Digital Angel relies directly on satellite transmission -- it doesn't use cell towers. The company is working on integrating relay devices into aircraft and ships. This would make transmissions easier and more reliable.

> As of May 2001, consumers can view and pre-order the biosensor watch and pager device. There are two watches, one for kids and one for adults. The components will be available in October 2001 for $299, and service will cost between $19.95 and $49.95 per month depending on the service plan you choose.

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