I have that same sort of lock on my back door but I bought that type on purpose. I was told that it is called a "panic lock" because it can be locked but still open from the inside. The idea is that, in the case of a fire or other emergency, the family can just go out of the door without fumbling with the lock while in a panic. I don't hide keys outside of my house because all thieves know about the fake rock, under the plant, IN the plant, the doormat and the brick moulding over the door trick. I simply never set foot outside unless my keys are in my pocket. If I'm going to be in and out a lot, I just unlock the door.