Mr. Anderson seems to be a bit paranoid -- of course, that's a good trait for someone tasked to teach students how to survive in adverse situations. His Whateley residence is surrounded by security monitors and other unspecified defenses, and is swept for bugs every few minutes in a random timer. He won't open the door until evaluating the probability of the person outside being, in fact, who it appears to be and the visit being peaceful. His home number is unlisted, and the students who know it also know that it's not a good idea to call it.