The house is personified in the story because it and the electronics in it are described as if they had feelings.
In this story, we have a post-apocalyptic world where almost every living creature has died. The house’s family is nothing but silhouettes in the paint on the side of the house. The house itself was fully automated though, and therefore it does not realize that the people are dead. It continues as if they are alive, even though it is personified as fearing that is people are gone.
Until this day, how well the house had kept its peace. How carefully it had inquired, "Who goes there? What's the password?" and, getting no answer from lonely foxes and whining cats, it had shut up its windows and drawn shades in an old maidenly preoccupation with self-protection which bordered on a mechanical paranoia.
This is personification because the house cannot really “keep its peace” the way a person would. Houses cannot inquire. Bradbury extends the electronic mind of the house to describing it as if it had actual feelings, because it has been programmed so well that it seems alive. This personification extends to the disembodied voice that seems to have fear. It also includes the only remaining inhabitants of the house, the robots.
The dog, once huge and fleshy, but now gone to bone and covered with sores, moved in and through the house, tracking mud. Behind it whirred angry mice, angry at having to pick up mud, angry at inconvenience.
The little robot cleaning mice do not really have emotions. Machines cannot think. However, Bradbury uses personification to describe them as angry that the dog tracked in mud, just like a person might be who had to clean up after it. The dog, the only living creature in the story, does not last long. It dies, and the robots just clean it up. Despite the personification, real life means nothing more to them than garbage.
This story is a cautionary tale about relying too much on technology. The irony is that the technology that made the humans’ lives easier is just an extension of the technology that killed them. The nuclear apocalypse is part of the technification of the country. The people were killed by technology, and technology lives on without them.