I live in a retirement community, and it continues to amaze me how many folks won't invest in a security/storm door for their entrances. Granted our door was almost 2k so they aren't cheap - but it looks innocent enough. I imagine a determined home invader would prolly be inside in less than a minute anyway - but this puts some safety glass between us and the riffraff walking the streets ...

Edited to add: I just scanned the original post and didn't notice the question about answering the door armed. That is, I guess, pretty much neighborhood-dependent. I certainly don't answer the door armed here - not to say it couldn't happen but there have been no home invasions in the 10 years this community has been open. I had two knocks at the door today - one from the neighbor next door and one from the (also) elderly lady living across the street. Again, if I lived out in a regular neighborhood I'd probably have to be more careful. And, a knock at the door after 10PM would cause me to be a lot more cautious...

Edited again: Forgot to say - good post OP! It's been interesting and good info to see how others handle the knock at the door situation. It's also refreshing to see, so far anyway, that no one has criticized other folks opinions and MO...