In Fahrenheit 451 how does Montag know that the Mechanical Hound leaves Faber's house alone?
Near the end of the book, Montag flees Faber's house, knowing full well that the Hound will track his scent all the way there. So, to try to mask his scent, he wears Faber's clothes, cleans things he's touched with alcohol, and has Faber turn on the sprinkler system in order to flush out any trail he might have left.
Montag flees the scene, but as he runs, he is able to
"peer through dimly lit windows of wakened houses...[at] people inside watching their parlor walls."
After Montag killed Beatty, the government sent out choppers and video cameras to follow the Hound's hunt. Using television, which everyone watched at night, they asked all citizens to look for Montag. They televised the entire chase, much like we televise car chases. So, all Montag had to do to figure out what was happening with the Hound, was look into the windows of the homes he passed. He was able to see the glowing "parlor walls" or television screens. If you have ever been out at night and someone has their blinds open, it is possible to see what they're watching on t.v. pretty clearly. It is this way that Montag sees the Hound approach Faber's house and sniff around, "and plunge away from Faber's house" alone.
I hope that those thoughts helped; good luck!