📖 The Quick Answer
Older systems analyze steering corrections and pedal behavior, alerting you to take a break ("Coffee cup" icon). Newer systems use an infrared camera aimed at the driver to track eye gaze, eyelid closure, and head pose. If the driver looks away from the road too long or shows signs of drowsiness, the system alerts and may even disable hands-free driving.
⚙ How It Works (Sensors and Algorithm)
Indirect systems track steering-wheel torque, pedal frequency, time-of-day, and trip length. Direct systems add an infrared camera (typically on the steering column or above the cluster) that works day or night. The camera runs gaze-estimation and eyelid-tracking algorithms. If gaze leaves the road for more than a few seconds, or if eyes close, the system escalates from a chime to a flashing warning to forced disengagement of hands-free driving.
🛡 What It Protects Against
Drowsy-driving crashes and distracted-driving crashes, which together account for tens of thousands of US crashes per year. AAA studies link drowsy driving to 16 to 21 percent of fatal crashes.
⚠ Limitations and When It Fails
Sunglasses, hats with brims, and certain lighting can confuse the camera. Indirect (steering-based) systems are easy to fool with light steering pressure. Camera-based systems are far more accurate but also raise privacy concerns. None of these systems are mandatory in the US yet.
🚗 Which Vehicles Have It
Required on US hands-free systems (GM Super Cruise, Ford BlueCruise, Tesla FSD Supervised). Increasingly standard from BMW Active Driving Assistant Pro, Mercedes Attention Assist, Subaru DriverFocus, Hyundai Driver Attention Warning, Toyota Driver Monitor.
🔧 Related TSBs and Recalls
Tesla and GM have issued OTA updates tightening eyes-on-road thresholds after federal scrutiny. Subaru DriverFocus has TSBs for false alerts when wearing certain sunglasses.