It is formed by metal material, study and durable in use. With chromium coating design of outer appearance and skidproof feature, it can highly reduce the possibility of chemical reaction like mechanical wear and chemical corrosion. The automatic locking retractor can ensure the safety as it automatically locks behind you within 3 seconds. We provide you with two methods to unlock the door once you install our smart lock. Besides the passwords unlocking function powered by AAA batteries, you can also use spare keys to open the door in case of emergency. For instance, the battery is wearing out. It is applicable to a variety of doors, such as wooden door, metal door, glass door, stainless steel door etc. The door thickness between 28-32mm is acceptable. Please note that two smart doors respectively with an app and a fingerprint scanner function will be rolled out soon. Please contact our customer service for further information.