A pet fence or fenceless boundary is an electronic system designed to keep a pet or other domestic animal within a set of predefined boundaries without the use of a physical barrier. A mild electronic shock is delivered by an electronic collar if its warning sound is ignored. The system was first invented and patented by Richard Peck in 1973 and was held until 1990 by Invisible Fence Co, now known as Invisible Fence Inc.
The pet wears a lightweight collar which emits a warning sound when the pet nears the boundary. If the warning is ignored and the pet crosses beyond the boundary of the fence, the pet receives a mild electric shock from the collar. The stimulus delivered to the pet may be applied more frequently and at greater strength as the animal approaches the boundary. The pet soon learns to avoid the invisible fence location, making it an effective virtual barrier. Animals (including humans) not wearing the collar are unaffected by the defined boundaries.
Although called "fences", these fence less boundary systems are more accurately termed electronic pet containment systems. In cost analysis they have shown to be much cheaper and more aesthetically pleasing than physical fences. However, an electronic fence may not be effective if an animal crosses a boundary while in a state of excitement. Pet fences are also used sometimes to contain livestock in circumstances where ordinary agricultural fencing is not convenient or legal, such as on British common land.
In some pet fence systems, there is a wire (which may be buried) that emits a radio signal to activate the receiver collar. Other pet fences are wireless. Rather than using an underground wire, they emit a radio signal from a central unit, and activate when the pet travels beyond a certain radius from the unit.
In another type, the collar uses GPS signals to determine proximity to a predetermined "virtual fence", without the need for any physical installation at all. This system allows some additional flexibility, such as simpler inclusion of "islands" within the containment area, and easier changes to the boundary, although location of the boundary is not as precise due to GPS tolerances.
In addition, some collars have multiple settings, allowing owners to have a collar emit a tone only, or one of several levels of static shock, with higher levels used to contain bigger, stronger dogs.
An underground fence is an electronic system to prevent pets from leaving a yard. A buried wire around the area to be used is energized with coded signals. A shock collar on the pet receives these signals. When the pet approaches the buried fence line, the collar makes a warning sound and then gives the pet a harmless electric shock. One popular brand claims more than three million installations.
The first commercial underground fencing system to contain house pets within a predetermined area was patented by Richard Peck, owner of Invisible Fence Company in 1974. Peck’s underground fence was also the first borderless containment system used to contain livestock. In 1987 Peck successfully contained domestic goats to a limited area using RF receiving collars intended for household dogs. Invisible Fence, Inc. is currently owned by Radio Systems Corporation. Further advances in technology have ensured that the safety of both dogs and cats is assured. Using a new FM digital technology DogFence Ltd are able to guarantee no false activation on the pets computer collar.
Underground fences cannot exclude other animals from the predetermined boundary. A dog contained within an underground fence can still fall prey to a larger dog or coyote, or even a person looking to harass or steal animals. This type of fencing does not have a warning mechanism to humans who might inadvertently wander inside the perimeter, making them more susceptible to dog bites/attacks. This type of containment is also not maintenance free; this system can only operate if the batteries in the animal’s collar are properly working. Finally underground fencing is not effectively accepted by every animal. Some pets become too afraid to wander into their yards out of fear of being shocked. If a pet is afraid to leave the yard it is usually a training issue. In Aug 2018 the British Government announced that all containment fences should be professionally installed to ensure the safety and security of both cats and dogs.
According to attorney Kenneth Phillips, electronic fences have downsides because children or other persons may still be able to approach dogs or other animals that are confined by such a fence, and the fence may cause the behavior of a confined animal to appear better than it actually is. In addition, an electronic fence may not be effective if an animal crosses a boundary while in a state of excitement.
Underground fences can be used on terrains or properties where it is not possible to traditionally fence. Modern systems are also suitable for cats and each year hundreds of thousands of cats go missing and are either killed or injured on the road. The underground fence can be used to secure driveways and open areas. Since the innovation of new training protocols for cats the underground fence has become a viable option for cat owners as well.
A 2016 Lincoln University study looked at the use of cat containment using electronic fences; reporting "No evidence of long-term welfare problems with electronic containment of cats". 
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