Entrances are one of the primatry ways of defending against the hostile animatronics.
In your Office there are a few entrances, those are:
-Doors on your left and right side,
-Vent on your left,
-Air Vent in front of you,
All of them can be closed, while doors and the vent will drain your power when closed,
the air vent will make your office temperature rise.
Note that while most of the animatronics can be prevented from entering by closing the entrance,
some of them might still try to get in or wait for the entrance to open.