I get back to my apartment with groceries & there's a guy with a backpack in the hallway by my door, apparently charging his phone although I didn't realize this at the time. We say hi and then I go inside, close the door, and lock it behind me. Nothing out of the ordinary. The guy didn't look dangerous; in fact he looked rather depressed and out of place. I was thinking about going back out to chat with him to see if he had gotten locked out or something. A few minutes later, after I had put up all the groceries, an old guy I've run into a couple of times finds him, they exchange words that I didn't make out through the wall (my computer is on the opposite of the hallway wall he was against), and then it's quiet again.
A few minutes later someone tried to open my door (which of course was locked) and then ring the door bell. I am, obviously, alarmed at this sequence of actions and head to the front door. I look through the peep hole and it's the old guy. I ponder my options for a second (ignore, fasten the chain then open the door, or just open the door a bit and see what he wants) then open the door a little bit while looking him over to see if there's anything threatening on him. Nothing on him, so I ask what's up. He then proceeds to tell me about the guy on the floor who was charging his Android phone yet didn't know anyone in the apartment building, and wanted to check in on me as he considers himself a caretaker for the place. He had a very offended tone about it as he said it so I tried to calm him down, saying it didn't seem like a big deal, electricity was cheap, and the guy probably needed to call someone. I've been in that type if situation, where my phone dies yet I am in critical need of contacting someone, so it didn't seem like something worth getting upset over. The guy certainly didn't seem threatening.
Eventually he sounded deflated, satisfied that I'm okay, and slowly moved away from the door. I bid him goodbye and closed the door.
I'm renaming the old guy to resident busy body now.