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