A key fob only tells you that someone authorized to a certain apartment entered. It doesn't tell you if it's the husband, wife, kid, mother in law who watches the kids on Thursdays, or friend who's taking care of the plants while you're on vacation, etc.

Key fob doesn't record the faces of visitors and for how long they have stayed.

Yes, except for the part about how they're dressed, what they're carrying, how they got there, who they said goodbye to on the sidewalk, etc., etc.