Keep your pet safe in your yard without burying wires! Just plug the Transmitter into a standard wall outlet close to the area where you want to contain your pet. Charge the rechargeable Receiver Collar in 2-3 hours. The Transmitter communicates with your dog's Receiver Collar and helps keep him in the designated area by first delivering a warning tone should he approach the containment perimeter and then by delivering a harmless but surprising electrical stimulation should he proceed further towards the containment edge. The system is portable, so you can bring it along with you! An unlimited number of pets can be added to the system as long as they wear a PetSafe® Wireless Receiver Collar.