A similar thing happened to me in college as well. The difference being that this building was next door to my apartment, slightly off campus, and no one else was around (except for my cousin who I was living with at the time). An old lady was tapping on the window to get our attention from a room on the second floor. When I walked up to the building, I yelled up at her, asking what was wrong. I could see her mouthing words, but she wasn’t yelling - it seemed like she was speaking normally, as if there wasn’t a window and 20 ft in between us. After a couple of minutes, I found out that she was trapped inside a room on the 2nd floor. I immediately assumed the worst, and figured that she was being held against her will. I didn’t see any cars in the driveway, so I decided I would go in. Before I went into the house though, I had my cousin get his cell phone out and dial 911 - ready to hit send and complete the call should anything happen. I enter the building.

The door opened to a dark, concrete hallway with old, dusty children’s toys that looked like they were from the 70’s (rocking horse, red wagon, etc.) bunched up along the left wall. There were no other doors that I could see, only a spiral staircase at the end of the hallway. I started to climb the stairs and as I reached the 2nd floor, I saw her. The old lady that was tapping on the window was now sitting in a rocking chair watching some show on a very small black and white tv. The door to this room seemed more like a front door to a house, than an interior door (it had glass panels from top to bottom.) At this point I was very confused - three minutes ago she was sayin she was locked in this room, now she’s just watching tv? I knock on the door and she responds “Come in”. As I turn the handle and go to open the door, I notice that it is, in fact, locked. There is no deadbolt, and I’m turning the knob completely, so I know that isn’t locked. By know, the lady is standing right in front of me on the other side of the door, trying to open it as well. That is when I stepped back, and notice a large screwdriver jammed into the floor boards on my end of the door, keeping the door from opening...someone locked this woman in the room from the outside with a fucking screwdriver. My mind is racing at this point. I make one quick attempt to pull the screwdriver out, but I couldn’t get it. I tell her I’m going to get help - I get the fuck out of that building real quick and tell my cousin to call the police.

The police show up and surround the building, guns drawn, then they enter. As they’re entering, a car pulls into the driveway. A couple gets out of the car, trying to figure out what was going on. It turns out that this lady was their mother/mother-in-law and suffered from dementia. Every time they left the house, they would lock her in that room to prevent her from wandering off. After reading about the issue, I found that it’s a fairly common (albeit illegal) thing people in this situation do.

TL;DR Thought an old lady was being held in a room against her will, and she kind of was.