PetSafe's In-Ground fence pet containment systems provide your pet with freedom and safety while costing thousands less than conventional fencing. It's quick and easy to install, reliable and safe, and with proper training, a very effective solution. A lightweight receiver is worn on your pet's collar, which picks up the signal and alerts your pet as he nears the underground boundary. Once your pet is properly trained, he will learn to stay in the boundaries designated by the radio fence. Includes 500 feet of boundary wire and 50 boundary flaps, enough to cover about one-third acre. For use in the US only. This unit is compatible with all US 110v outlets and are not to be used with 220v international voltage.