I carry everyday, so if I'm dressed I'm armed. If I'm not dressed I don't answer the door.
I also lock the storm door, when I am home. When I do answer it(after looking from another window) I know who is there and I don't open the door for strangers or door-to-door sales people. My large dog is usually faster to the door than I am, while I'm looking out the window, he's already at the door. His social skills aren't the best and he's not going to roll out a welcome mat.