Instead of a firehouse dog, like a dalmatian, each firehouse now has a mechanical hound. Describe it.
The hound is like a robotic dog. Like a dog, the hound can track people by smell. It is programmed by the firemen to track someone based on their body chemistry. The hound is used to track down fugitives. It is equipped with a long needle that it can use to inject its victims with to immobilize them.
Bradburn describes the hound in the following passage.
"...brass and the copper and the steel of the faintly trembling beast. Light flickered on bits of ruby glass and on sensitive capillary hairs in the nylon-brushed nostrils of the creature that quivered gently, gently, gently, its eight legs spidered under it on rubber-padded paws."
Montag has several encounters with the hound. The time readers learn of the hound is when it growls at Montag in the firehouse. Later after he burns Beatty, the hound attacks him and injects his leg. He is able to escape, the firemen send another hound after him. Faber, and later Granger, help him to change his scent to lose the hound.