Green’s Dictionary of Slang

1. (US black) an eye, usu. in pl.

1923		T.A. Dorgan in Zwilling TAD Lex. (1993) 121: He got to dreamin’ he was directin’ traffic on Fifth Avenue and hit me right on the peeker.
1944		D. Burley Orig. Hbk of Harlem Jive 28: With my deuce of fine peekers, I dig ole St. Nick.

2. a spyhole, i.e. in a door.

1942

D. Burley N.Y. Amsterdam Star-News 13 June 16: She laid her gims through the peeker [...] and slammed the slammer tight.