In a device for monitoring tire air pressure in motor vehicles with a sensor that delivers a signal corresponding to the deformation of the tire, and with an evaluating unit that detects the signal from the sensor, the sensor is so designed such that it delivers an electrical pulse corresponding to the degree of deformation of a tire, especially deformation during a footprint pass. The evaluating unit determines the degree of deformation as a function of the height of the amplitude of the pulse or the evaluating unit determines the degree of deformation as a function of the ratio of the duration of the pulse to the duration of one wheel revolution.