1. A method for ascertaining an alertness of a vehicle driver, characterized by the steps: detecting a potentially dangerous situation by a system of the vehicle; detecting at least one optical feature of the vehicle as a reference point, the at least one optical feature having a known position on the vehicle; receiving at least one image recorded by a camera unit; estimating a visual observation field of the vehicle driver by comparing the at least one image with the position of the at least one optical feature; and detecting the alertness of the vehicle driver by comparing an orientation or a position of the potentially dangerous situation to the visual observation field of the vehicle driver.