According to non-canon "Legend" material — that's the stuff that's not officially part of the "Star Wars" narrative any longer, but was written before the "Star Wars" story group was formed to manage the tales and the timeline — bad guys had to keep their eyes open for retribution-minded rebels. To that end, the Galactic Empire and Galactic Republic employed security droids like the BT-16 Perimeter droid, made by Arakyd Industries.
These droids were equipped with sensors and blaster cannons to deter or annihilate intruders. They were also among Jabba the Hutt's most prevalent hangers-on, prowling about his lair keeping tabs on the comings and goings of Jabba's shady business partners.
The BT-16s were also delightfully weird — some of them featured a conspicuous clear globe on the undersides of their central body element. Inside that globe? The brain of a B'omarr Monk.
The order of the monks was known to remove brains from colleagues who reached a state of enlightenment, disconnecting them from their bodies and suspending them in the form factor of a droid. Then the monk ambled about in the motorized body, free of his/her physical manifestation and able to spend each moment meditating on the universe.