An agonizer used by the Terran Empire during the 23rd century
An agonizer was a small device worn on the belts of Imperial personnel used to inflict pain for minor transgressions. More severe offenses called for using the agony booth. (TOS: "Mirror, Mirror")
The Terran Rebellion continued their use to great effect. In 2372, Kira Nerys and Elim Garak were subjected to these machines by their captors to make them more obedient. These agonizers were vastly improved over the older models, to point which they no longer needed physical contact with their victims to be effective. (DS9: "Shattered Mirror")