SmartLeash® is the FIRST and ONLY retractable leash that automatically stops your dog when he or she tries to suddenly run or lunge. SmartLeash operates like a regular retractable leash unless your dog tries to run — then Smartleash locks, quickly, safely and automatically. Like a seatbelt! It stays locked as long as your dog has tension on the leash. When your dog releases tension, SmartLeash resets instantly, ready to protect your pet again. SMALL: Up to 22lbs