Customer Service: We offer customer service that responds within 24 hours. If you have any questions about our door locks, please feel free to contact us; we offer customer service 365 days a year. Tips: The fingerprint door handle requires 4 AAA batteries (not included), which last up to 8–10 months depending on usage frequency. Low battery reminder function (the red light flashes three times when unlocking); equipped with a USB interface, which can be used for backup power. Easy Installation: The keyless door lock is designed to fit US standard doors, with a backset of 2-3/8″ (60 mm) and 2-1/8″ (70 mm) and a door thickness from 1-3/8″ to 2-1/8″ (30 mm–55 mm). The lock installs quickly and easily with just a small screwdriver. Suitable for both left- and right-handed doors (suitable for indoor and outdoor doors). Multiple Access Methods: 4-in-1 biometric door lock suitable for everyday life. Code unlock, 4 key fobs, and fingerprint unlock – no need to carry keys or worry about searching for keys everywhere. A mechanical key can be used as a backup key for unlocking (in emergencies, such as a dead battery). Fingerprint Sensor: 508 DPI fingerprint sensor module, 360° fingerprint reading is accurate and fast, supports storing up to 100 sets of fingerprints, and the recognition rate exceeds 99% within 0.3 seconds.