What does Montag receive from Faber before leaving his house? How is this item supposed to guide him in his conversation with Captain Beatty?

What Faber gives him is “a small green-metal object no larger than a .22 bullet,” which Montag says looks like a Seashell radio. In fact, this is an in-ear receiver/transmitter, which will let Faber listen to Montag’s conversations and speak to Montag privately. This “green bullet” is part of Faber’s plan to exercise influence over all the city’s firemen, and it will let him “hear and analyze the firemen’s world, find its weaknesses, without danger.” He says he can “put out ears into all parts of the city, with various men, listening and evaluating.” So, on the surface, Faber plans to listen in on Montag’s conversation and give Montag advice as he tries to outwit Beatty. In reality, Faber shows that he plans to manipulate Montag just as directly as Beatty does, and that this manipulation is part of his plan to reshape the city’s approach to books and learning. This “green bullet” system of influencing firemen would help to undermine the book-burning system and, as Faber sees it, restore learning to the world. Montag seems to recognize that he is being manipulated when he says, “I’m not thinking. I’m just doing what I’m told, like always.... When do I start working things out on my own?” Nonetheless, he accepts Faber’s guidance and follows his advice.

When Montag visits Faber's home in part two, he attempts to gain Faber's help comprehending the literature he is reading. Montag also asks Faber to help him overthrow the fireman structure. Faber initially tells Montag that he is not interested in challenging the fireman structure, because it would be dangerous and useless. However, Montag ends up getting Faber's attention by ripping pages out of the Bible. After Faber begs Montag to stop, he agrees to help him challenge the fireman agency. Faber then leads Montag to a hidden room in the back of his home and gives him a two-way communication device called a "green bullet." The green bullet resembles a Seashell radio and allows Montag and Faber to communicate in an inconspicuous manner. Using the green bullet, Faber can listen in on Montag's conversation with Captain Beatty. Faber, a literary expert, can talk to Montag via the green bullet and tell him how to respond to Beatty's persuasive arguments.