Abstract: A breath tester includes an electronic detector providing an information signal with an amplitude level which varies as a function of the alcohol content in the breath under test. An anomaly detector circuit stores a signal related to the peak of the information signal, and continually compares this peak value with the instantaneous value of the information signal. When the difference between the peak signal level and the instantaneous signal level exceeds a preset amount, the output display of the breath tester is modified to indicate the analysis process has been disturbed by an anomalous chemical substance.

Abstract: In a breath tester of the type wherein a subject blows breath into an input for a predetermined continuous and uninterrupted flow, which breath is exposed to an electronic detector element whose output signal is employed to derive and display an output which is representative of the alcohol present in the breath and which detector, if subject to continued exposure of additional breath after the predetermined flow, is prone to produce an erroneous output, an electronic system is provided for electrically storing and isolating a detector signal produced from only the predetermined flow, whereby errors resulting from continuous flow or mechanical valving arrangements are avoided. The system disclosed includes circuit means for switching out and holding the end of flow detector signal and for producing an output based on that signal.