I'm going to attempt to answer this without pirating any information from the internet. I worked briefly for a house arrest technology provider, and the term "geo-fencing" was actually used to describe the specific perimeter outlined for an offender. Essentially, if you had a sexual predator, a gps chip in a provided device would geo-fence schools, playgrounds, etc by a minimum of 1000 feet. If the offender were to cross over the line, the gps geo-fence would be crossed, initiating a red flag.

Hope this helps!

Brent Kettler Replied on Oct. 9, 2011

My answer is pretty high level. For additional depth, do a Google search for a company by the name of "Scram." Once on their site, do a site search for "geo-fence."

Howard Gunn

CIO,CTO,VP,Director, BST Technoloiges

Posted on Oct. 10, 2011

Brielle

You may be familiar with wireless or virtual fencing that uses terrestrial radio sensing. If the animal crosses the line their collar might give them a shock to get them to stop and change direction. The system may also alarm or notify a central control. These virtual fencing applications are typicall done physically on terrestrial radio systems or buried wires. They can be enabled by low cost RFID types of chips and scanners.

Geo fencing allows boarders to be established virtually, around a GPS device. Devices within the virtual boarders can be assigned to alarm or notify the central security if they go outside of the assigned area. Brent described a use to identify a device entering a defined restricted area. Both types of geo fencing are enabled by GPS devices with no terrestrial investment or infrastructure.

In many cases, the geo fencing area can even be initiated by the device (example parent defining the playground area with an alarm notification should the child wander outside of the area) or the network (example security personal managing the area where a contractor is authorized versus an area that is not authorized).

I am not sure if carrier GPS triangulation tracking is being used for geo fencing applications. Most systems I have seen or heard of use satellite GPS. Some devices have both types of antennas and receivers (cellular frequencies for talking and data and satellite for GPS tracking and geo fencing).

Hope this helps.
Howard Gunn