In a method and a device for detecting the drowsiness of a driver in a motor vehicle, a drowsiness model is provided to determine a value characterizing the drowsiness of the driver as a function of at least one output quantity of a driver-activity sensor array. Moreover, the device for detecting drowsiness includes a brightness sensor as well as a correction model for correcting the value characterizing the drowsiness of the driver as a function of at least one output quantity of the brightness sensor.