A method for detecting characteristic movements of a vehicle driver for diagnosing a lowering of vigilance by the driver. In a preliminary phase, the surface of the seat base and of the backrest of the seat is divided into a plurality of elementary surfaces in each of which is embedded a pressure sensor able to detect the pressings and releasings applied by the driver on the pressure sensor, and a plurality of specific movements is selected, each of which includes the determination of at least one geographic zone subjected to a "pressing" or a "releasing" resulting from the movement. The data processing includes analyzing the measurement signals provided by the pressure sensors and comparing, at each sampling time, the possible detected geographic zones of pressing and releasing with each stored geographic zone, in order to provide information on detection of a specific movement when there is a correlation between the geographic zones.