Solenoid
A Solenoid was a technological component.
The Second Doctor described an audio lock as a solenoid switch only operable by use of a particular sound. (TV: The Space Pirates)
The Third Doctor effected the use of solenoids in Bessie's remote control system. (TV: The Dæmons)
Sutekh described his selection for a logic puzzle in the Pyramid of Horus as the "extreme right solenoid". (TV: Pyramids of Mars)
The revival mechanism utilised by the Tharil slavers in E-Space was activated using a solenoid. (TV: Warriors' Gate)
The Fifth Doctor posited the malfunction of the TARDIS as attributable to the solenoids in its lateral balance cones. (TV: The Visitation) He later disabled an android by cutting its solenoids. (TV: The Caves of Androzani)