"any small gadget," 1909, American English, of unknown origin. For the "love-bite" sense, see hickie.
Entries linking to hickey
hickie n.
"love bite; mark on skin made by biting or sucking during foreplay or sex," 1934; earlier "pimple, skin lesion" (c. 1915); perhaps a sense extension and spelling variation from the earlier word meaning "small gadget, device; any unspecified object" (1909, see hickey and compare doohickey, still used in this sense).