I had a very brief decisive encounter with a pizza delivery guy one night about 2:00am. My screen door was unlocked, my front door was unlocked and he was totally at the wrong house (don't know that I had ever forgot to lock it before or since). I had heard something strange at the door and as I approached it I noticed it unlocked, as I reached for it, he started opening the door. He ended up laying on my porch and I ended up apologizing for knocking him down (I did not point the gun at him and I did keep my finger off the trigger, so that's something). He was dressed like pizza guy, had uniform, pizza, car with sign on it, flashlight, etc. I believe him that he couldn't find the address and saw my lights on and tried knocking. I had my headphones on, so didn't hear him until he really started banging on the door. For the life of me I don't know why he tried opening the door. I know I would not try opening a stranger's door, especially at 2:00 am, especially in my neighborhood.
Now I do what I suggest you do, I lock my storm door. If someone is knocking on it, I can open my interior door if I l want to and talk to them through the storm, or not open my interior door. It's not hard to yank the locked storm door open, but it's loud and takes intent.
Wait... I can get a pizza delivered at 2am?!? From where?