Abstract: A breath testing system for under-supervised or unsupervised alcohol intoxication breath testing. The system includes a breath input unit, a controller which delivers a sample of deep lung breath to an evaluator including an alcohol detector and an output apparatus. The controller includes a breath flow sensing means, e.g., a pressure sensitive switch and timer, to require a predetermined and essentially continuous and uninterrupted breath flow prior to testing to thereby insure that alung breath sample is tested. Means for signaling failing or passing of the test are provided. A passing signal cannot be obtained unless the predetermined continuous nnd uninterrupted flow has occurred and the resulting sample tests below a predetermined alcohol concentration. The system is disclosed in one environment of use: in a motor vehicle, wherein failure to take or pass the test modifies the operation of the vehicle (e.g., prevents it from being driven or governs its maximum speed).