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. 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. Completely wireless & portable Add an unlimited number of pets with additional wireless Add-A-Dog® Receiver Collars (sold separately) Over Stimulation Protection: Stimulation stops after 30 seconds Uses 1 x 6 Volt battery (included) Collar size: Fits neck sizes 15 - 71 cm Covers an adjustable circular area up to 1/2 acre/20 ares/0.2 hectare (55 metres in diameter) System Includes Transmitter with Power Adaptor Receiver collar for neck sizes 15 cm to 71 cm Operating and Training Guide Battery (PetSafe® RFA-67D-11) 50 Training Flags Test Light Tool