Q. Is it permitted to seclude oneself with the opposite gender if the door is open or unlocked, but there is no realistic expectation of anyone coming in? One knows with 100% certainty that no one is going to come in (for example, the people who usually come in are out of town, or it is an apartment of a person who never has guests and never has anyone come to his house, and has no realistic expectation of anyone barging in)?
A. Horav Shlomo Miller’s Shlit’a opinion is that if the door that opens to the street or to a hall in the building, where individuals walk occasionally including the hall, is left partially open it is permitted.
One may also ask a neighbor that has an entry key, to occasionally and randomly come and check on him.
Additionally, one may use a cell phone or laptop that has a camera focused on the main area in question. If left turned on, he may ask someone else in another location, to occasionally check on it, without the knowledge of the one’s being watched.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a.