Abstract: Visual methods and systems are described for detecting alertness and vigilance of persons under conditions of fatigue, lack of sleep, and exposure to mind altering substances such as alcohol and drugs. In particular, the intention can have particular applications for truck drivers, bus drivers, train operators, pilots and watercraft controllers and stationary heavy equipment operators, and students and employees during either daytime or nighttime conditions. The invention robustly tracks a person's head and facial features with a single on-board camera with a fully automatic system, that can initialize automatically, and can reinitialize when it need's to and provide outputs in realtime. The system can classify rotation in all viewing direction, detects' eye/mouth occlusion, detects' eye blinking, and recovers the 3D(three dimensional) gaze of the eyes. In addition, the system is able to track both through occlusion like eye blinking and also through occlusion like rotation.