An Eymorg control bracelet
A control bracelet was a device worn upon the wrist of Eymorg inhabitants of Sigma Draconis VI. It had several functions, such as the ability to control the operation of a pain band, and to render an individual unconscious. It was so powerful that it could affect the entire crew of a ship.
The Eymorg leader Kara used this device to render the entire crew of the USS Enterprise unconscious when she sought to steal Commander Spock's brain in 2268. (TOS: "Spock's Brain")