I hardly answer unknown knocks during the day, let alone at night. I just peek and see what they are doing. If it is one of my neighbors, I will assist. (You really need to get to know your neighbors and look out for each other. I know my entire cul-de-sac on a first name basis).
If it is a stranger, most likely it ends up being a door to door sales guy. If it is at night most often it's someone up to no good. I've heard enough ridiculous excuses (you mean, you travel all the way to a strange neighborhood with no phone and no money for gas, and all of a sudden need to use my home phone? LOL ya right.). In that case I ask them to politely leave and that my finger is ready to dial 911. Never tell someone you are armed. IF they get in to harm you, it will be through a kicked in door. In that case they will be met with lead.