PetSafe 250M Dog Receiver Collar. This PetSafe Dog Receiver Collar is designed so that you can add an extra dog onto the 400M trainer and operate these from the same remote. Simply add an extra collar to the Petsafe 250m kit to expand to a 2 or a 3 dog system. Easy to program an seconds and totally waterproof. This collar can be used with either the PetSafe 250m trainer or 400m training collars.