Transistor

A transistor is an object both found and mentioned throughout the Fallout series.

Fallout Tactics

 * The Reavers mention transistors.

Fallout 3

 * In the "A Broken Robot" random encounter, the Lone Wanderer can remove all transistors related to "basic operations" on a malfunctioning Mister Handy, rendering it inoperable.
 * In the "Slavers Escort" random encounter, the Lone Wanderer can attempt to free slaves from slave collars. One of the possible outcomes found in the game files mentions tweaking a transistor to disarm them.

Fallout 4

 * In 2023, Jack Cabot utilized transistors to create a portable version of the Abremalin field generator.
 * A soldier stationed at the Listening Post Bravo had a transistor radio.
 * Proctor Quinlan mentions that he would rather miss a transistor radio than a synth.

Fallout 76

 * A memory transistor is used during the quest The Messenger.
 * Scott Conroy attempted to chase down cryptids in Appalachia, and brought along a General Atomics BS7 transistor radio while doing so.

Behind the scenes

 * In June 2003, originally on the Interplay Forums, developer Joshua Sawyer pointed out that integrated circuits are likely used in robots, as they are affected by electromagnetic pulse weaponry in Fallout. In a follow-up statement on tumblr in March 2019, Sawyer maintained his position on transistors in Fallout, reiterating how robots in the series are affected by EMP blasts "so the state of technology isn't represented consistently."
 * In 2016, in a Ubisoft livestream's closing Q&A, developer Joel Burgess stated that transistors were never invented in Fallout. He elaborated on how miniaturization is not a priority in the Fallout world, and how technology advanced despite the lack of it.
 * In 2018, in an interview with YouTuber Matt Barton on the first Fallout game, developer Leonard Boyarsky stated that the choice to stay with vacuum tubes instead of advancing to transistors was intentional, commenting that without transistors, enemies "wouldn't be as susceptible to an EMP blast."
 * Concept art in the Fallout: New Vegas Official Game Guide Collector's Edition describes Mr. House's helmet apparatus, stating that it was designed to be potentially "fitted with transistors."