EASYPET Add-on/Spare Collar for KoolKani In-ground/Underground Pet Electronic Dog Containment Fence System Add-on collar for KK-9000 or EasyPet EP-8000 dog fence containment system; SAFE INTELLIGENT WIRELESS FENCING: Progressive Tone & Vibration StimulusA warning beep tone with vibration will be issued first, and more intense beep tones with vibration will be followed, then a pulsed stimulus if your dog continues to move closer to the boundary; WATERPROOF DOG TRAINING COLLAR RECEIVER WITH LASTING RECHARGEABLE BATTERY: Collar Receiver Unit Rechargeable & Fully Waterproof The collar receiver is rechargeable and fully waterproof (submersible). NO LIMITS ON ADD-ON COLLARS: Multiple collar compatibleAdd as many collars as you like. There is no limit to the number of collars it can control.