The costs to the public and to the offender associated with drunk driving are huge.  When someone is pulled over and tested by a breath analyzer, that test is followed up by a blood draw (usually at a hospital), which produces a more accurate measurement of ethanol in that sample.  It is widely recognized that the breath analyzer is an inexpensive screening device, but that it is not specific for ethanol.  Other alcohols, such as isopropanol, and some ketones, such as acetone, can interfere with the breath analyzer, because it is a simple electrochemical fuel cell.  The measurements of the blood sample use more sophisticated (and expensive) instruments.

The problem comes when breath analyzers are used inappropriately as ignition interlock devices designed to keep people, who have been found guilty of drunk driving, from starting their car until the breath analyzer says they are not drunk.  Given all of the possible interferences outlined above, it is not uncommon for people to not pass the test.  In addition, there is a considerable cost to the driver associated with these interlock devices.  They should really be measuring only ethanol, but given their design, they generate a lot of false positives.  It seems only fair that these interlock devices be required to demonstrate that they are measuring only ethanol and not some unknown interfering compound.

A word on my background:  I have a Ph.D. in analytical chemistry from the Massachusetts Institute of Technology (in 1968).  I was on the staff and faculty of MIT’s Chemical Engineering Department until 1979, when I became a professor of chemistry at Indiana University.  I am a Fellow of the American Chemical Society, the American Association for the Advancement of Science, and the Society for Environmental Toxicology and Chemistry.