A transport scrambler (or pattern scrambler) was a device that would disrupt a transporter beam. This could prevent someone from leaving or entering an area covered by the scrambler.
In the year 2268 the Gorn shipyards on Seudath had transporter scramblers as part of the defense system. A scrambler was also activated in the Klingon Imperial Intelligence safe house in Tzoryp when the intruder alert alarm was activated. (VAN - Declassified novella: The Stars Look Down)
During the Klingon siege of Gornar of 2402-2403 the Gorn erected a network of transport inhibitors to prevent the KDF from landing troops. This network failed on Stardate 80344.81, and the royal palace fell to General Klag twenty-eight hours later. (ST website: The Path to 2409)