Shock Collar: Unsurprisingly used (because in a universe with extensive automation possibilities and, moreover, the ability to use perverted sophotechnology to edit people into compliance, the only reason to go for conventional slavery is sadism For The Evulz) by the absolute worst of the Galaxy’s slaver civilizations and subcultures; usually, the kind that stimulates the brain directly into pain and pleasure, thus causing brainwashing and the slow and nasty kind of crazy-going.

Possession (in most places) or use (absolutely everywhere vaguely civilized) of one is, obviously, a very capital crime indeed.