Ossus Stone Guardians, which are also called Jedi defense droids, were a type of droid designed to look like simple statues. They were commonly found in Jedi temples built around the time of the Qel-Droma Epics.
These uncomplicated droids were capable of remaining motionless for millennia without needing any upkeep. They would only move when their sensors sensed a danger. At that point, these strong machines would attack every target within their designated zone. Because they operated with very simple programming, the majority of them couldn't tell the difference between allies and enemies. The droids possessed strong armor and, at times, the droid's frame had layers of cortosis beneath the thick stone that covered the outside. However, the droids had a vulnerability: Jedi who knew about it could use the Force to activate a shutdown switch located inside the droid's body.
By the time of the Imperial Era, they were protecting the Neer's Gauntlet and the Greelwood Saber inside the Vault of Justice, which was located in the Great Jedi Library on Ossus. In addition, inside the Chamber of Antiquities, the skeleton of a Draethos was still lying at the base of his large chair in his office, and two stone guardians stood silently as guards to keep the chamber safe from anyone who might break in.