Most fourth class droids were not programmed to speak and interact with organic beings. The KX-series security droid was an exception, though it was not proficient when compared with a protocol droid, whose capabilities were similar to that of the T-series and its successor, both Confederacy tactical droids.
- Star Wars Propaganda: A History of Persuasive Art in the Galaxy
- Star Wars: Rogue One: Rebel Dossier
- Star Wars: The Visual Encyclopedia (First identified as fourth-class droid)
- Star Wars: Droidography