Nobody ever knocks but people occasionally ring the buzzer. It usually makes me jump out of my skin because our buzzer is kinda loud and has about the same pitch as a fire alarm. Aside from that, it wouldn't bother my SA too much because most of the time when someone rings our buzzer it isn't even for us anyway (unless I'm expecting a package). It's usually some inconsiderate twit coming to see one of our neighbors and they press all of the buttons for some unknown reason. So it's just the sudden "RED ALERT!" sound that scares me. I'm jumpy anyway.