What happened to Montag's green bullet?

Montag’s green bullet fell out of his ear when Beatty struck him a blow on the head. Beatty picked up the green bullet, listened to Faber, and then he switched it off.

“Well---so there’s more here than I thought. I saw you tilt your head, listening. First I thought you had a seashell. But when you turned clever later, I wondered. We’ll trace this and drop it on your friend.” Said Beatty.

Later, Montag burnt the bullet up with the flamethrower.