No batteries. No key. Always works. Super robust and sturdy. I installed this at a remote beach house where if you lose the key or lock yourself out, you hope you have your car keys and head home. This ends that fear. It is an incredible piece of mechanics! Installation is a breeze with various hardware to fit differing door thicknesses. Clean design that covers BOTH the door knob and deadbolt holes too! Love this! Highly highly recommended.
brain freeze 
