How is the mechanical hound used by firefighters in Fahrenheit 451?

The mechanical hound is a modern, robotic version of the old fire mascot, the Dalmatian.  Dalmatians have been used in fire houses not only as a mascot but as dogs that run alongside horse-drawn fire engines of the past.  Dalmatians were also used to warn people when fire trucks were leaving the station; they would go out and bark to alert people to the emergency.

The mechanical hound in Fahrenheit 451 serves a purpose that is darker than the original Dalmatian mascot.  The mechanical hound is able to sniff out books and people who have books.  If it catches someone with books, it will inject the person with a sedate that renders one helpless.  It looks like a spider with eight legs and constantly “hums”.   The mechanical hound is used as a weapon for this modern fire department that destroys rather than saves unlike the friendly Dalmatian mascot known today.