PetSafe Stubborn Dog Add-A-Dog Extra Receiver Collar. This extra Receiver Collar can be used to add another dog to any PetSafe In-Ground Fence system or as a replacement collar to the Stubborn Dog In-Ground Fence system. This collar is not a complete system and needs to be used with a compatible transmitter. Key Features Highest intensity level available Features For dogs 3.6 kg and up Fits neck sizes 15 - 71 cm 4 adjustable levels of static stimulation Tone with vibration mode alerts your pet with a beep Over Stimulation Protection: Stimulation stops after 30 seconds Covers up to 13 ares (1/3 acre/0.13 hectares) with included boundary wire For stubborn or hard-to-train dogs Waterproof Uses 1 x 9 Volt battery (not included) Battery usually lasts 1-3 months Good/low battery indicator Compatible with PetSafe® In-Ground Fence system.