Abstract: A drunkometer in which the rate of airflow toward an alcohol vapor sensing device in an input channel is sensed mechanically or electrically, and a resulting flow signal is integrated. The direction of airflow in the input channel is also sensed either by photoelectric means or by a negative-temperature-coefficient resistance and an error signal is furnished if the direction of flow corresponds to inhaled breath. A validity signal signifying that the measured value is a value representative of the concentration of alcohol in the bloodstream is furnished if the integrated signal representing the total exhaled air volume exceeds a predetermined minimum value before an error signal is furnished.