Extra collar receiver with ReadyTest function to ensure a proper fit * For use with Innotek"s IUC-4100, IUC-4200, and IUC-5200 systems * Delivers electronic stimulation dogs quickly learn to avoid * Low-battery indicator; collar fits neck sizes 8 to 24 inches * Receiver measures 2-3/4 by 3/4 by 1-1/4 inches; limited lifetime warranty