The Master Lock No. 4401DLH Bluetooth Padlock features a 2-7/32in (56mm) wide metal body for durability. The 11/32in (9mm) diameter shackle offers 2in (51mm) vertical clearance and is made of boron alloy, offering maximum resistance to cutting and sawing. The smartphone/app interface offers speed, ease of use, & greater control with the ability to share access, with keyless convenience. The locking mechanism features anti-shim technology, offering maximum security and there is a 2-piece weather cover for maximum outdoor protection. And don't worry about the battery running out. There is backup access using directional code on lock keypad; low battery notification & reminder on padlock and in app; and a battery jump that allows for temporary access if battery dies while locked. It comes with an easy to replace CR2 battery.