In Fahrenheit 451 what is the effect on Montag when the old woman on Elm chooses to die with her books?
When the woman chooses to die, it makes Montag question the way he's living and ultimately spurs his interest in books.
When the firemen arrive to burn down 11 No. Elm, Montag thinks that usually the perpetrators have already been taken by the police -- led away bound and gagged. The firemen don't usually deal with them. He feels the woman on Elm is spoiling the ritual by being there and talking to them. Montag thinks:
The police went first and adhesive-taped the victim's mouth and bandaged him off into their glittering beetle cars, so when you arrived you found an empty house. You weren't hurting anyone, you were hurting only things! And since things really couldn't be hurt, since things felt nothing, and things don't scream or whimper, as this woman might begin to scream and cry out, there was nothing to tease your conscience later. You were simply cleaning up. Janitorial work, essentially. Everything to its proper place. Quick with the kerosene! Who's got a match!
The presence of the woman makes him uneasy. When a book falls into his hands, he glimpses a line that says "Time has fallen asleep in the afternoon sunshine." He thinks to himself that it wasn't done on purpose as he hides the second book under his arm.
Montag asks the woman to come with him, even when the other firemen are ready to leave her there to burn. She refuses. She tells him to leave and when he gets outside, she strikes her own match and sets the house on fire, burning with her books.
That night, he feels ill and questions his relationship with his wife, his career, and everything he's ever done. He feels something other than pleasure at the idea of burning books for the first time, saying:
"Last night I thought about all the kerosene I've used in the past ten years. And I thought about books. And for the first time I realized that a man was behind each one of the books. A man had to think them up. A man had to take a long time to put them down on paper. And I'd never even thought that thought before."
He realizes he undoes all of that work in mere minutes. Montag changes his life from that day on, beginning to read and finding a mentor in Faber.
The old woman, who lights the match that leads to her own demise, is a catalyst for great change in Montag's life. When he met Clarisse and was so moved by her, and realized after speaking to her that he was not happy at all, he started thinking and pondering the reason why. Then he comes across this woman who would rather die with her books than live without them. This floors Montag--why would she possibly want that? He puts two and two together in his mind--he is miserable, and this lady loves her books so much that she won't live without them. He thinks that possibly, somehow, books have to have the key to happiness. He has never met anyone before who was willing to fight for something they believed in; this woman was, and it made him think that perhaps she had some answers.
It is the old woman's death that sends Montag on a journey to find out exactly what it is about books that brings meaning to life. He is so impacted that he is ill in the bathroom when he gets home, can't sleep that night and is sick the next day. In comparing his life to the old woman's, he asks himself, "How do you get so empty? Who takes it out of you?" He feels like he is spinning out of control and describes it as being the "victim of a concussion" or being "thrown from a cliff" or being "whilred in a centrifuge." He realizes, after the old woman kills herself, that something had to change. He had to find answers.
The next day, he starts to read books and seeks out Faber, who he feels can help give him answers. Montag begins his journey of self-discovery, revelation, and eventually, revolution. I hope that those thoughts helped; good luck!