GPS-Fencing
In 1997 Robert E. Marsh of AgriTech Electronics patented a fenceless animal control system using GPS location information. In Marsh’s device a portable unit is attached to each animal and includes a GPS receiver which provides an audible signal and an electrical shock. Each portable unit further includes a suitable battery and appropriate electrical circuitry. The portable unit also contains signal processing components necessary to convert the GPS signal into location information and a remotely programmable memory database that receives and stores the desired boundary parameters. Circuitry within the portable unit compares the GPS defined location information with the predetermined parameters and activates an audible signal; and if necessary, an electrical shock will be delivered, when the collared animal approaches the defined boundary.
Read more about this topic: Invisible Fence