The law against “Yichud” (seclusion) is normally understood in orthodox Jewish law as preventing a man and a woman (who are not married, nor family members) from being together alone in a room.
Given the bevy of women who traipse to my headquarters to receive brachas, rachmones and things, the law of yichud is one reason I keep my live cam on 24/6.
Moral accountability is my motto!
Reb Moshe had a liberal understanding of this law. As long as the door wasn’t locked and there were people in the vicinity (in the same apartment or office or synagogue building), you weren’t violating the law of yichud.
Reb Moshe was pretty liberal with his own observance of this mitzvah.
He was theoretically correct — take it from me, I am a great Torah sage! — but it is not what is done anymore in Orthodoxy.
Rabbi Mordecai Tendler was also pretty liberal with this mitzvah.
When Rabbi Steven Weil took over at Beth Jacob, he installed small windows in all the office doors so people could walk over and look in and see what was going on.
Steven Weil’s fore-runner, Abner Weiss, probably had good reasons for keeping his door shut against public view.