Why did Faber believe that Montag died during his altercation with Captain Beatty and the hound?

Faber believed Montag was dead because the audio-capsule stopped working.

Montag said, "I've been a fool all down the line. I can't stay long. I'm on my way God knows where."

"At least you were a fool about the right things," said Faber. "I thought you were dead. The audio-capsule I gave you--"

"Burnt."

"I heard the captain talking to you and suddenly there was nothing. I almost came out looking for you."