What would you do if someone knocked on your door in the middle of the night?

We were watching a movie yesterday night when we heard a loud knock(sounded more like slamming) on the door. We asked through the door who was there, but no one answered. We checked to make sure the back door & all windows were locked. We turned the outside lights on too. It really got my heart racing. My first thought was that it's probably some neighborhood s***heads messing around, but I read an article online that it could also be a tactic for home invaders to see if anyone is home. Our area is relatively safe, but I do recall that a couple of years ago our neighbors across the street had their car stolen...TWICE.

My friend said we shouldn't have even said anything & just remained quiet, but I don't know if I agree with that, wouldn't you want the person to know that people are in fact home so they don't try anything?