Best way to handle a late night knock on your door

Have all you "tough" fellows with your shotguns and 9mm ever considered what kind of trouble you would be in if you shot someone in a rest stop or parking lot? If it turned out person knocking was unarmed, you would be alive but spending the rest of your life and all of your assets paying for that minute of macho. And as others have said, you point the firearm at a police officer, you may never point another firearm again because you could be DEAD.