The Master Lock No. 4400D Bluetooth Padlock features a 1-229/32 In. (47Mm.) wide metal body for durability. The 9/32 In. (7Mm.) diameter shackle offers 7/8 In. (22Mm.) vertical clearance and is made of boron alloy, offering maximum resistance to cutting and sawing. The smartphone/app interface offers speed, ease of use, and greater control with the ability to share access; with keyless convenience. The locking mechanism features anti-shim technology, offering maximum security. Comes with easy to replace CR2450 battery. Battery jump allows for temporary access if battery dies while locked. Locker Mode setting allows for storage inside a locker. The 1 year limited warranty provides peace of mind from a brand you can trust.