Throughout the book, references are made to the tiny "Seashell" radios that virtually all citizens wear. These allow them to continue their consumption of empty entertainment even when they are away from TV. Montag discovers that he hates the seashell radios because of how they keep people apart; this mirrors Bradbury's own experience seeing people unaware of their surroundings because of small radio earphones. Late in the book, Montag uses a modified seashell to keep in touch with Faber, and it also picks up on the general bands.
"We have mobilized a million men. Quick victory is ours if the war comes...." Music flooded over the voice quickly and it was gone.
"Police Alert. Wanted: Fugitive in city. Has committed murder and crimes against the State. Name: Guy Montag. Occupation: Fireman. Last seen..."
(Bradbury, Fahrenheit 451, hrsbstaff.ednet.ns.ca)
He hears these two announcements which herald the end of his life in the city. The war, which has been alluded to many times, is finally happening; he hears that announcement later on a conventional radio. Montag understands the critical need to escape; he knows the power of modern weapons and respects that the enemy probably has weapons of equal power.
The other announcement is repeated in different forms as Montag flees. The radio mobilizes the citizens of the city to help the government find and kill Montag; he is dangerous because he is an individual, not a drone like the other citizens. By reaching every citizen at once, the government is almost able to catch Montag several times.