What takes place between Montag and Beatty? What does Beatty discover?

Having just arrived at his own house in response to a fire alarm, Montag is numb with disbelief. His coworkers rush into his house as Millie, who turned him in, rushes out and hurries by without a word. Captain Beatty needles him, chiding him for thinking he could keep his books concealed and asking why he didn't turn them in when the Hound came sniffing around.Beatty discovers the "grren bullet" or listening device in Montag's ear. This will be the final showdown between Beatty and Montag.