What in the book is symbolic of computerized law enforcement in Fahrenheit 451?
Certainly the flame-thrower and the Mechanical Hound are the most overt examples of computerized law enforcement. The Hound is programmed to locate both books and people; this establishes the connection that books bind people together and technology drives them apart.
Also, there are the television parlors; Millie's "4th wall" and the equipment the technicians use on Mildred. This is underscored when Mildred is less concerned with the war; more concerned with how the war may interrupt her television programs. She is much more in tune with machines than she is with Montag. References to technology are analogous to enforcement and to pacify the masses (television and drugs).
When Montag leaves the city, he is leaving the mechanical society behind. The suggestion is that books keep us more in touch with other humans and supposes that technology can play a role in isolating humans from each other and diluting their emotions.