These were created in the good ol' days, by engineers. Unlike modern sentries, they couldn't be picked up. They had three levels. First and only appearance was TFC Team Fortress Classic, with Jerma and Star.
The modern sentries. Much more stable and high-tech than last time, they can be easily picked up and stored in other areas. They can be healed by hitting them with a wrench, and by placing them near dispensers. Like classic sentries, that also have three levels.
These imps of Al Guru are miniature sized sentries, with faster building time and shooting. They are known for killing enemies in mere seconds, often causing Star to hit his keyboard and bring up Windows Help and Control.