Agonizer

An Agonizer was a device used in the mirror universe by the Terran Empire's Starfleet to punish their members for relatively minor offenses. More serious offenses - such as attempted mutiny or assassination - were punished with the agony booth.

In the 23rd century, agonizers were worn on a person's belt, and could be demanded by a superior officer in that officer felt a person had committed an infraction. When the agonizer was applied to a person's body it would cause intense pain which could bring a person to his or her knees. (TOS episode Mirror, Mirror).

In the Dark Mirror version of the mirror universe, agonizers were still in use by the Terran Empire, and had been refined to the point that they were incorporated into the Starfleet insignia worn on a person's uniform. (TNG novel Dark Mirror).