Abstract: A method and apparatus for measuring a blood alcohol content value by means of a breath alcohol concentration as well as for securing the reliability of this measured value. The apparatus comprises: sensor elements (1) for obtaining a measured alcohol concentration value from an incoming exhalation air stream; sensor elements (1) for obtaining a measured carbon dioxide concentration value from the same exhalation air stream (9); as well as first output elements (2) for producing, if necessary, a result proportional at least to a blood alcohol content.

Abstract: An apparatus for determining the alcohol concentration in a gas mixture, which may contain a number of such interference components that have substantial absorption within the range of the alcohol absorption line to be presently determined, by means of a method based on the absorption of infrared radiation. The apparatus comprises: a radiation source (1); a chamber (4) for receiving a gas mixture (6) to be measured, said chamber being provided with windows (7a, 7b) whereby a radiation (2) passes through the gas mixture; a detector (13) which receives the radiation having passed through the gas mixture and transforms it to an electric state for further processing; between the radiation source and the detector an optical interference filter (10), which has a narrow radiation transmission band and which is pivotable (P) relative to the main traveling direction of radiation for changing the wavelength range of the filter's transmission band.