The delay in knowing what happened outside the house builds a sense of foreboding. The eeriness of the ordinary functioning of the house as it goes about its everyday business without inhabitants builds a sense of unease. Words choices Bradbury makes add to the feeling that something is not right. For example, the words "empty" and "emptiness" are used to describe the house in the first paragraph. Later, we find the word "waiting" and "wait" repeated twice as the garage door opens but nobody gets in the car to drive away. Saying the eggs were "shriveled" and the toast like "stone" continues to build up ominous imagery that something has gone wrong.
The busy activities of the house, with its nonstop activity, seem pointless and disconnected without human presences, showing the difference between the reasoning mind of a human being and the mindless programming of a piece of technology.
It is only as we are led outside to the garden sprinklers washing the side of the house that we find out that the paint has burned off the building, leaving only the imprint of the inhabitants outside, working or playing. It is at this point that we begin to realize that nuclear devastation has probably hit the area.