In a method and in a device for detecting when the driver of a motor vehicle becomes tired, the tiredness is determined as a function of a detected steering inactivity phase and a subsequent steering action. In this context, the steering inactivity phase is logically combined with the steering action, and the logic combination is stored at various times. The logic combination is stored with an assigned weighting factor, and the weighting factor is determined as a function of a classification of a steering situation.