After Marcus Scarman was killed by Sutekh in his tomb, Ibrahim Namin brought several Osiran service robots to Priory House in England in sarcophagi. The robots were confined to a locked wing of the house but had been active for some time. They killed Collins, the butler, when he entered the room. Namin activated the robots once more in order to search for and destroy Warlock and his rescuers, the Fourth Doctor and Sarah Jane Smith.
After Namin was killed by Sutekh's puppet, the animated corpse of Scarman, the robots were used as workers and guards. They set up a force-field around the house and constructed an Osiran war missile to free Sutekh from his bonds. They also killed several people on the property, including a poacher who attempted to interfere.
Scarman took one of the service robots to the Pyramids of Mars on the mission to find and destroy the Eye of Horus. As part of one of the Pyramids' tests, two of Horus' Osiran service robots would appear when an intruder was trapped in a Tachotron Crucible: One robot would lie, while the other would tell the truth. Another one of Horus' robots also guarded the chamber where the Eye of Horus was located, and fought with Scarman's robot over the Eye. (TV: Pyramids of Mars)
The Guardian of Truth and Guardian of Lies robots were encountered by Bernice Summerfield in a pyramid on Mars. The Guardian of Lies used the voice of Bernice's dead husband Jason Kane when interacting with Bernice, as it said it would calm her down. (AUDIO: The Pyramid of Sutekh) Ace and Benny found one whilst looking for an Eye of Horus. (AUDIO: The Vaults of Osiris)
The service robots were powered by a cytronic particle accelerator in the shape of a pyramid that was located on the back. They took voice commands from whoever they were programmed to obey. A special ring was used to activate them or countermand their orders. They were also extremely strong, able to manhandle humans with ease, and could easily strangle someone. (TV: Pyramids of Mars)