This smart door lock successfully saves the replacement cost in the case of damage to the door lock. It only needs to replace the lock itself, without any electronic circuit and any change on the door. It is very suitable for some ancient buildings that do not allow too many changes, and it is also suitable for small hotels and small offices to solve access control problems. The installation process is also very simple. The installation can be completed without professional guidance. It is also easy to learn. The length of the lock can also be adjusted, and locks can be selected for different doors.