The Aperture Science Sentry Turret, or simply known as sentries or turrets, is a Personality Construct-based gun platform used throughout the Aperture Science Enrichment Center. 

The Aperture Sentry Turret has a single red eye, sleek appearance, and predominately white color scheme common to most Aperture Science technology. Sentry Turrets are commonly seen serving as guards in the maintenance areas of the Enrichment Center. The Personality Core of the Sentry Turret is located within the outer shell, right above the guns. 

It speaks in a childlike voice, often saying polite things, even apologizing after it kills someone.