Unlike the Sentinel, they did not possess bipedal feet but rather used four wheels for locomotion. They also possessed a single visor eye and no discernable mouth. Two arms were used to interact with their environment and to utilize an energy rifle for defense or attacks.
They did not demonstrate the ability to speak and seemed subservient to the Sentinel guards.
The true nature, ranking and capabilities of the Guards were never explored and its entirely possible that they are simple programmed machines rather then a sentient construct like the Transformers.
Generation 1 cartoon
When the Dinobots accidently arrived on Cybertron through the Space Bridge, they took over the Decepticon Headquarters along with Shockwave. When this happened, the Guards were called and a large battle was fought between the five Dinobots and the Decepticon automatons. Despite destroying many of them, the Dinobots were overwhelmed and were captured except for Swoop. Later, when Spike Witwicky and Carly arrived on Cybertron and escaped Shockwave's grasp, a group of Guards would accompany a Sentinel in locating them. After they were captured, they were sent to the Cybertonium Pit where they were watched until a fight broke out between Spike and Grimlock. After lowering the shield in order to remove the Humans, the Guards were attacked by the Dinobots with Slag's fiery breath attack melting them.