|Technician: Engineer||Tier 1|
|Basic (1 pt): The cost of deploying a sentry gun is reduced by 5%.|
|Ace (3 pt): Your sentry guns gain a protective shield.|
- The name of the skill is a reference to the third law of robotics. While it remains more or less faithful to its namesake up to the point of letting a sentry gun protect itself better with an increased ammo pool and shield, it also indirectly violates the law and the two preceding it at the same time by allowing the sentry to harm and kill humans.