An Eymorg pain band
Activated pain bands
Pain bands are belt-like devices used by Eymorg individuals to inflict pain upon enslaved Morg individuals on Sigma Draconis VI. The primary function of this was to keep the enslaved Morg under control. The Morg were obidient out of fear of the pain inflicted upon them when the pain bands are activated. Pain bands were activated by a control bracelet worn by an Eymorg.
While held in captivity by the Eymorg James T. Kirk, Leonard McCoy, and Montgomery Scott were exposed to the pain caused by pain bands several times. Eventually, Kirk managed to deactivate their pain bands using Spock's brainless remote-controlled body.
The practice of using pain bands was probably abandoned after, Spock's brain, which had served as the controller of the subterrainean Eymorg complex. (TOS: "Spock's Brain")