The PetSafe Deluxe In-Ground Cat Fence has been proven safe, comfortable, and effective for all cats over 6 lb. and at least 6 months old. The system works by producing a radio signal from the Fence Transmitter through up to 4000-Feet of Boundary Wire. The Boundary Wire is buried or attached to a fixed object to enclose the Pet Area. You temporarily define this Pet Area with Boundary Flags for a visual aid in training your cat. Your cat wears a Receiver Collar with Contact Points that touch his neck and, once trained, is allowed to roam freely in the Pet Area. When your cat reaches the Warning Zone, the Receiver Collar gives a warning beep. If your cat continues into the Static Correction Zone, a safe Static Correction will be delivered through the Contact Points to get his attention until he returns to the Pet Area. 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.