Green’s Dictionary of Slang

1. (US) a police or private detective’s badge; thus by metonymy, the policeman or detective.

1891		A. Day Mysterious Beggar 219: You’re a buzzer.
1903		St Louis Post-Dispatch (MO) 8 Feb. 17/1: [He] touched the ‘buzzer,’ putting Desmond ‘next’.
1914		Jackson & Hellyer Vocab. Criminal Sl. 22: buzzer [...] Current mainly in western circles. An officer’s badge or star, the insignia of authority. Example: ‘Who are you? says he. For reply I flashed my buzzer.’.
1925		D. Hammett ‘The Scorched Face’ Story Omnibus (1966) 80: Pat flashed his buzzer. Though the black man had poor English, he had knowledge of police badges.
1939		R. Chandler ‘Trouble Is My Business’ in Spanish Blood (1946) 181: ‘I’m a private detective.’ I showed him a buzzer.
1946		J. Evans Halo in Blood (1988) 133: A snooper, hunh? I should of caught on when you didn’t flash a buzzer on me.
1951		M. Spillane One Lonely Night 82: I flashed my buzzer.
1953		C. Boeckman ‘Tough Cop’ in Margulies Back Alley Jungle (1963) 112: Grimm took out his buzzer and flashed it.
1960		(con. 1950-1960) R.A. Freeman Dict. Inmate Sl. (Walla Walla, WA) 22: Buzzer – a police badge.
1971		N. Smith Gumshoe (1998) 23: I always carry my buzzer — the clubs I’ve not been a member of that it’s got me into!
1978		W. Diehl Sharky’s Machine 270: Sharky showed him his buzzer [...] The General looked at the badge.
2023		(con. 1962) J. Ellroy Enchanters 140: My DA’s buzzer hit him nonplussed.

2. (US black) a warning (of time).

1938

Pittsburgh Courier (PA) 30 July 11/1: Jack, they just laid the buzzer on me so I must nix this scribe.