Many pet owners experience a variety of problems inside the home caused by their pets getting into areas that the owner would like to keep them out of.  For example, dogs getting into trash cans, cats climbing on tables and both cats and dogs climbing on couches are examples of such problems. 
To combat this problem, electronic transmitter/collar systems have been used.  Such systems operate by producing an electromagnetic field in a spherical pattern.  This requires a significant amount of power in order to generate a strong enough field.  Therefore, this has necessitated that the transmitter be an alternating current powered unit that is supplied from a wall outlet. 
However, many of the locations that owners desire to keep their pets out of are not necessarily located next to a wall outlet.  Therefore, to locate a transmitter in one of these locations would require that power cords be run across the room from the wall outlet.  This is clearly an undesirable solution.  For example, couches located in the middle of a large room or a significant distance from a wall outlet cannot be easily supplied with A/C power.  As another example, keeping dogs from drinking out of a toilet is difficult to achieve as many bathrooms do not have wall outlets located close to the toilet.  In addition, even though wall outlets may be located close to some areas, it is often desirable to use the wall outlets for other items.  For example, there are often wall outlets located close to a bed (which one often desires to keep a pet off of); however, those outlets are preferably used for clock radios and reading lights.  Consequently, the A/C powered units are oftentimes very inconvenient to use. 
While in many instances a single transmitter will suffice for protecting an area of the home.  In some instances it is desirable to protect a larger area than can be accommodated with a single unit.  In that situation, it can sometimes be difficult to use more than one unit to protect the large area.  This is due to the fact that the units transmit the same signal in a spherical pattern.  When placed near one another, the signals produced by the transmitters can cancel.  When the signals cancel one another, a dead zone is created in which the pet can move freely.  This may be the very place that the pet owner wants to keep the pet from entering.  As a result, the effective use of two units close to one another which are transmitting the same signal is sometimes difficult to achieve. 
Another difficulty encountered by pet owners is that not all of their pets need to be kept away from certain areas.  For example, a pet owner's unruly dog may need to be kept away from the front door in order to keep it from jumping up on guests.  However, that same pet owner would like the pet cat to be able to enter the zone by the front door.  With a system in which the dog's collar and the cat's collar are both triggered by the transmitter signal, it is not possible to create selective zones around the door.  Thus, such a system suffers from the fact that it cannot accommodate different avoidance zones for different pets in the same household. 
While many animals are capable of being trained to leave an avoidance zone if they enter one, there are sometimes a few that are not deterred by the correction signal used.  For example, in some cases, an increasing intensity of the correction signal has been used to cause the most stubborn of animals to leave an avoidance zone.  The intensity can only be increased to a maximum intensity—especially for commercially sold systems that must accommodate a diverse group of animals of different sizes.  Thus, in the past, one had to accept that for those animals that could not be deterred by the maximum intensity correction signal that the system would not be as useful.