In the time of the Great War, the Autobots use security probes to patrol Cybertron's underground. Spheroid in form, these probes float about at a gentle pace and possess a visual sensor which can be extended on a jointed arm, for better examining items of interest. They are each armed with an Energon repair ray for defense.
Starscream, Thundercracker, and Skywarp encountered a number of security probes as they invaded the Cybertron underground via Kaon Cliffs. The probes were not much of a problem for three hardened Decepticon warriors, but it's entirely likely that they were able to alert the Autobots ahead of the incursion.