BREATHALYSER

A method for determining the alcohol content in the exhaling respiratory air using an alcohol measuring instrument and measuring the alcohol content when the exhaling air transmits the determined value of the alcohol concentration. This determined value of alcohol concentration occurs when the time variation related to the height of the alcohol signal is below a predetermined threshold value and the velocity of flow of the exhaling air is above a given value and is maintained without interruption for a given time. The apparatus includes an infrared measuring instrument which is connected into the respiratory air current and measures the alcohol concentration of the exhaling air. This value is applied to an indicator through a linear gate when an AND-gate is triggered by threshold comparators and a timing element activated by a threshold comparator.