These keypad locks are a great innovation. Useful for my kids so they don’t have to carry a house key. Even my five year old knows the code and can open the door. Would also be excellent for AirBnB uses because you can program 250 codes and the app notifies you when someone opens/locks the door. It took about an hour to install, including programming. Directions were clear and all parts were labeled well. Uses 4 AA batteries. Best part is I was able to key the new lock to my original lock so my house keys still work the same.