This extra receiver collar can be used to add a cat to an existing PetSafe® In-Ground Fence or as a replacement collar to the In-Ground Cat Fence System (PCF-1000-20). Our smallest collar features a special safety stretch section that flexes with your cat's movements. Features For cats 3.6 kg and up Fits neck sizes up to 29 cm Tone-only mode alerts your pet with a beep 4 adjustable levels of static stimulation Over Stimulation Protection: Stimulation stops after 30 seconds Waterproof Collar uses 1 3-volt battery Battery usually lasts 1 month Good/low battery indicator Compatible with the In-Ground Cat Fence System (PCF-1000-20)