Innotek Extra Receiver For UltraSmart, CONTAIN N TRAIN Extra collar receiver for UltraSmart IUC-5100 In-Ground Fencing System Enables 2-dog training for pets 6 months or older; contoured for comfort Lightweight, waterproof, and rechargeable; collar fits neck sizes 8 to 24 inches ReadyTest indicates perfect fit, plus system and battery status Measures 2-3/4 by 3/4 by 1-1/4 inches; limited lifetime warranty