An electronic scrambler was a device used to interfere with electronic signals.
In 2267, Spock constructed an electronic scrambler to disable an alien entity called the Companion. The Companion was chiefly composed of ionized gases and electricity; Spock's device was designed to scramble its electronic impulses.
Spock's scrambler was very simple; a red on-off switch near the right side of the front panel was the only important control. Upon being activated, it elicited an immediate response from the Companio, who sought and destroyed the device, very nearly killing Kirk and Spock in the process; only Zefram Cochrane's intervention prevented it from doing so. The device ultimately did not cause the creature any permanent harm. (TOS: "Metamorphosis")