You know, this actually happened once when I was home alone. My parents decided to take one car. Since my dad's truck was in the driveway, they must've thought somebody was home. I heard knocks at the door, but I'm not allowed to open the door if there's no adults home. So they tried to knock again, and again, and again, until they just stopped. Apparently, they left us an ad for their church in the door handle, as discovered by my parents when they got home.