This is a routinely done thing at the university residence when I lived there (each floor has a lock like this at the elevator room and the staircase doors). Ot

This is a routinely done thing at the university residence when I lived there (each floor has a lock like this at the elevator room and the staircase doors). Other common items are like a small stack of paper in a folder, or whatever. People did this so they don't have to get their friends by going from their room to the elevator or stairs.