Electronic animal restraints use radio signals and specialized collars or harnesses to keep animals within a given area, or to control them without a leash.
There are three ways that these are set up.
The most common uses a single-strand wire that is run along the boundary of the area the animal is to be kept in. When the animal approaches the wire, the collar either emits warning tones, vibrates, or both. If the animal lingers near the boundary or attempts to cross it, the collar either constricts or produces an electric shock.
Another method creates a zone where the animal is permitted by using a weak signal. If the animal strays outside of the area where the signal reaches, the collar either shocks or constricts.
Some systems also allow for mobile use, in which case the animal's owner carries a small transmitter that shocks the animal when a button is pressed.