Standard-Issue Information Retrieval units are assigned only to Irken Invaders. They obey every command that they are given, and can be altered and reprogrammed at their master's or mistress' will. They can speak, despite not having mouths (with the exception of GIR).
SIR Units can be given markings to distinguish them from other SIR units, as shown with MiMi, having an Irken emblem on her forehead. They are very deadly, due to the fact that they have an assortment of weapons at their disposal and jet-boosters installed in their feet (with an undocumented fuel powering those boosters); as a result, any that malfunction can be lethal to both Irken and enemy alike.
They seem to be made out of a metal that is both highly durable and flexible (unlike any metal created on Earth), as they are able to change the shape of their eyes to form facial expressions, and GIR is able to move and manipulate his mouth to form words. In one of the cancelled episodes, GIR survived being hit by a car without gaining any injuries whatsoever.
In "The Nightmare Begins," the Almighty Tallest Red stated that SIRs can also double as thermoses, but GIR has never seen turning into one. This may because the empty space in GIR's head that is supposed to be a thermos is usually filled with random junk like beehives, cupcakes, or salted nuts.
SIR Unit Code
The SIR Unit Code is a law of the Irken Empire covering SIR Units and their freedom. It is only mentioned in GIR Goes Crazy and Stuff. As explained by GIR in duty mode, the code enables a SIR Unit's free will in the event that they and their master's mission is under threat.
Known SIR Units
- Despite his "malfunctioned" status, GIR is a SIR unit with the usual weapons, except for that the fact that he has a mouth, cyan markings, and a defective brain. His name is apparently an acronym, although he himself states that he doesn't know what it means. Because he is made of trash, it could possibly stand for "Garbage Information Retrieval", though it hasn't been proven. GIR was made of broken parts of SIR units from a trash can made by the Tallest for Invader Zim. His brain consists of lint, a paperclip, two coins, a screw and a gumball (as seen in "The Nightmare Begins"). Unlike other SIR Units, GIR's torso is not divided into two segments, suggesting that GIR's body is that of a previously-used model of SIR unit.
- MiMi is a feminine-programmed, modified SIR unit custom-made by Tak. She is distinguishable from standard SIRs by the emblem on her forehead and the large, extendable claw that replaces her right arm. She also seems to have a white chestplate and dark blue shoulders.
- Invader Skoodge's unnamed SIR (pictured) assisted with the conquest of Blorch.
SIRs (except modified SIRs, such as GIR) come in a standard look and with standard weaponry, including:
- No mouths
- About two feet tall; it is possible that the Irkens' choice of making their servants so small was influenced by their culture's obsession with height.
- Missile Launchers
- Assortment of Guns (such as Plasma Disk Launchers)
- Catapult Launcher
- SIRs are technically without sex, but are almost always programmed to have either male or female genders, much like the droids of the Star Wars franchise.
Mishaps with SIR Units
There was one situation in "Megadoomer" where Invader Tenn was attacked by malfunctioning SIR Units that were supposed to have been sent to Invader Zim, but the destinations were switched by a rebellious slave worker. It cost her the mission, and (had the series continued) would have led to her being taken prisoner by the Meekrob, forcing the Irken Military, Zim and Invader Skoodge to rescue her.
Interestingly, all the malfunctioning SIR units act almost exactly like GIR.
- In "Megadoomer," the defective SIR's have voices that sound like GIR's (except they're voiced by Wally Wingert, Kevin McDonald, and others), which may imply that GIR's voice pattern is a normal part of his defectiveness.
- In "The Nightmare Begins," the first SIR Unit given talks, despite SIR Units don't have mouths.