A method for passive
breath alcohol detection, the method comprising: A) passively obtaining a first
air sample from the air inside the interior of a vehicle; B) determining the concentration of (i) a tracer gas, and (ii) an
analyte present in the first
air sample; C) passively obtaining a second
air sample from the air inside the interior of the vehicle; D) determining the concentration of (i) the tracer gas, and (ii) the
analyte present in the second air sample; E) continuing to passively obtain an N number of air samples from the air inside the interior of the vehicle, and for each air sample obtained, determining the concentration of the tracer gas and the
analyte present in the air sample; F) determining a number of peaks in the concentration of the tracer gas and a number of peaks in the concentration of the analyte present in each of the air samples; G) determining a
confidence interval based on the number of peaks in the concentration of the tracer gas and the number of peaks in the concentration of the analyte; and H) controlling operation of the vehicle based on a function of the
confidence interval and the concentration of the analyte present in the air samples.