Green’s Dictionary of Slang

breaker n.2

[the code-word breaker, signifying one’s desire to join a conversation]

a Citizen’s Band radio enthusiast; thus used as a term of address to initiate a radio conversation.

[US]Time 11 Jan. 39/2: 10-4, Marcie... Oh-oh, here’s a breaker; come in, breaker, and identify yourself [OED].