Answer:
Montag is lost in thought and is surprised to look up and discover that the fire truck stopped in front of his own home.
Explanation:
Fahrenheit 451 is a dystopia that presents a society where having books is prohibited and firefighters are responsible for setting fire to houses that have books. This society encourages the use of TV that alienates people and does not stimulate their ability to reason.
Montag is a firefighter and is dissatisfied with the situation in which he lives, in relation to marriage, society and work. He keeps books hidden in his house and one day, he finds out that he has been denounced and that he will have to burn down his own home. This moment is being narrated in the passage shown in the question above.