Not sure if I'd hear them if they were banging on the door. The main door is downstairs, under the balcony and the "real" front door. If I believe the person I'd let him/her in. Depends on how they say it and what they look like, i.e. their expression.
If it's someone I know and trust, I would probably let them in.
If it's someone I don't know and/or trust I would probably get awkward and tell them to try my neighbours or something, because I wouldn't understand why they'd come here out of all of the houses in this street. If they have tried other houses and they refused to help, I'd see that as a red flag.
I don't know what I'd do. I'd like to think I would help someone, but I'm fairly certain I'd be really paranoid in that situation. I'd at least call the cops and bring a baseball bat to the door. Granted, I live on the third floor of my apartment, so unless it's someone who is living on this floor, I'd be pretty skeptical. Even then, my apartment manager lives on this floor, so I'm sure they'd go to him instead of me.
If I'm at my parents' house, I'll let my dad deal with it (with a gun).
._. This also makes me realize that if this ever happens while I'm living with my boyfriend, he'd let them in the house in a heartbeat. ...I should look into learning how to use a gun.