The Question and Answer section for Fahrenheit 451 is a great resource to ask questions, find answers, and discuss the novel.
I'm sorry, this is a short-answer forum designed for text specific questions.
The doors were programmed to work by touch.
He put his hand into the glove-hole of his front door and let it know his touch. The front door slid open.
From the text:
The old man admitted to being a retired English professor who had been thrown out upon the world forty years ago when the last liberal arts college shut for lack of students and patronage.