PetSafe, Wireless Pet Fence, Innovative, Portable System, No Wires To Bury, Just Plug The Transmitter Into An Out Of The Weather Electrical Outlet Close To The Area Where You Want To Contain Your Pet, Transmitter Emits A Radio Signal Up To90' All Directions, Communicates With Your Dog's Receiver Collar & Helps Keep Him In The Area You've Designated For Him, Portable, So You Can Bring It Along With You, Unlimited Number Of Pets Can Be Added To The System As Long As They WearA PIF-275-19 Receiver Collar.