This is the replacement Collar Receiver for W-227 Smart Dog In-ground Pet Fencing System. It is among the most reliable, cost-efficient pet containment systems available today. A buried wire transmits a harmless radia signal. When you dog approaches the boundary, the signal causes the dog's collar receiver to deliver a warning beep first. If your dog continues closer t the boundary, the system will issue a mild shock. If your dog continues further, hte system will issue stronger shocks until your god returns to within the boundary you have set up. Your dog will naturally seek to avoid correction, and is content staying within established boundaries.