PetSafe's Stubborn Dog In-Ground radio fence pet containment system provides your pets that are stubborn or hard to train with freedom and safety while costing thousands less than conventional fencing. Recommended for dogs 30 pounds and up. It's quick and easy to install, reliable and safe, and with proper training, a very effective solution. A lightweight super receiver is worn on your pet's collar, which picks up the radio 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.