Solenoid

A  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)