A personalized device for monitoring a motor vehicle driver is disclosed. The personalized device includes a device for measuring a driver monitoring parameter and a control unit that is programmed to estimate a state of alertness of the driver in accordance with an estimation rule and the measured value of said monitoring parameter, and determine said estimation rule in a personalized manner for said driver in accordance with a set of driver-specific data comprising at least said measured value of the monitoring parameter and multiple sets of predefined data, each of which corresponds to a predefined group of drivers.