Question:
May one seclude himself with a lady if the door is unlocked/ open but there is a 0% chance that someone will barge in (such as one who is in his apartment and he never has guests or people that come in there, and there is no realistic expectation that someone will come in)?
Answer:
If there indeed is 0% chance that someone will come in than that is what we call yichud, and it is not permitted. Even in the woods, or a deserted area, where things are more open than just a door, it is still yichud of there is no fear that they will be seen or interrupted.
