A car can detect drowsiness in a number of ways, the most common being through sensors that monitor eye movement and head position. These sensors are usually located in the steering wheel or dashboard, and they work by tracking the driver's gaze to see if their eyes are drooping or if their head is nodding off. Other systems use heart rate monitors or skin conductivity sensors to track the driver's physical state and look for signs of fatigue. Some cars even have cameras that watch the driver's face to look for telltale signs of sleepiness.