The sentry droid version seen on Lothal
Patrol droids, also known as sentry droids, were droid units that served as guards in numerous locations. Their design and function often mirrored those of probe droids.
During the Galactic Empire's control of Lothal, a specific type of sentry droid was put into service, patrolling Imperial facilities. The Lothal droids typically operated in groups of three and bore a resemblance to the observation droid used by the Galactic Republic during the Clone Wars, due to the presence of a prominent, central red photoreceptor and an antenna. However, the Imperial model deployed on Lothal had an integrated blaster with its barrel sticking out, allowing it to rotate. The Galactic Empire made use of IMG-099 Imperial Mark IV patrol droids for scouting and surveillance on planets, including the streets of Mos Eisley on Tatooine.
The Empire also utilized DT-series sentry droids, which were also employed as guards and combat training droids.
The patrol droids belonging to the First Order were positioned in and around the installations of Starkiller Base, and they included a long-range communications antenna.