Petsafe, Stubborn Dog Receiver Collar, Extra Receiver Collar Can Be Used To Add Another Dog To Any Non-Rechargeable In Ground Fence System Or As A Replacement Collar To The Stubborn Dog In Ground Fence, Features 4 Levels Of Static Correction At A Higher Intensity Especially For Stubborn Or Hard To Train Dogs, For Dogs 8 LB & Up, Waterproof, Uses 9V Battery Not Included.