Let me start by saying that sometimes I can, uh, be careless. I don't usually read the instructions first. Just dive in. The battery cover is held in place by a locking mechanism that requires a push of a button to open. I didn't notice the button and couldn't move the door. Finally I opened it with a screwdriver. *Then* I noticed a button. Nothing was damaged except my pride, which testifies to the strength of the doorbolt. WHY you need a lock, no idea. I have a couple of UV-A/B metersβ¦