Breathalyzer and Breath Test Accuracy
The "Implied Consent" laws of California provide that if you are arrested for drunk driving, you are presumed as a condition of the privilege to drive to have impliedly consented to chemical testing. If you refuse to submit to testing, your driving privilege can be suspended. The chemical test will normally consist of your choice of breath or blood analysis; a urine sample can be taken instead if neither breath nor blood are readily available.
The most commonly used test is breath analysis. Although generically referred to as a "breathalyzer" (the brand name of one of the earliest models, manufactured by Smith and Wesson), California police agencies use a variety of different makes and models of breath machines - usually at DUI sobriety checkpoints or at the police station. However, all have one thing in common: they are prone to a wide variety of problems and are reliably inaccurate (see the discussion of "Breathalyzer Accuracy" on this website). And an experienced attorney specializing in DUI defense should have the expertise necessary to find the flaws in a given breath test and to demonstrate for a jury the machine's defects.
To cite but one example, breathalyzers are controlled by a primitive computer which calculates the blood-alcohol level of the subject by assuming he/she is average in all ways despite the fact that individual physiology and alcohol metabolism varies greatly (they do not, for example, distinguish between "he" and "she", despite the fact that alcohol metabolism varies considerable between the sexes). In fact, you may be surprised to learn that these machines do not even measure alcohol! Most use infrared spectroscopy technology to detect the presence of a "methyl group" in the molecules on a subject's breath. However, thousands of chemical compounds contain the methyl group in their molecular structure. Studies have documented over 100 of them on the human breath, including acetone (found in diabetics and people on diets) and such products as paint, thinner, glue, gasoline most of which can be breathed in as vapors or absorbed through the skin (to be breathed out hours later and registered by a breathalyzer as "alcohol").
Analysis of a blood sample for alcohol is generally more accurate than breath analysis, but problems exists with this method as well: lack of sterilization, preservatives and/or refrigeration; coagulation; vial mix-ups; fermentation of the blood in the vial; etc.