Innotek UltraSmart Extra Collar Receiver for IUC-4100, IUC-4200, and IUC-5200 Systems 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