Wikia

Sentries were fourth-degree droids used to guard important installations.

The Sentry was a repulsorlift combat droid encased in a glossy, spherical shell not dissimilar to that of the IT-O Interrogator, and was the combat equivalent of the Viper probe droid. Armed with a rapid-fire blaster and heavy deflector shields, the Sentries also had a defensive mode with a metallic grid covering their hull when not firing.