This hidden fencing system is among the most reliable, cost-efficient pet containment systems available today. A buried wire transmits a harmless radio 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 to the boundary, the system will issue a mild shock. If your dog continues further, the system will issue stronger shocks until your dog returns to within the boundary your have set up. Your dog will naturally seek to avoid correction, and is content staying within established boundaries.    Include AC adaptor for Transmitter.