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Morgan wrote:.... I was told that if you were acting stone cold sober but had any alcohol in your system, you could be charged ....

That would be a pretty harsh, since you always have a measurable amount of ethanol in your blood (your body makes it), albeit usually a very low amount (probably below what breath analyzers can detect). Breath analyzers don't measure blood alcohol content; rather, they estimate it from the presence of certain chemical structures (methyl groups) in the exhaled breath. Lots of things other than alcohol can cause those structures to appear in the exhaled breath: smoking, diabetes, paint, adhesives, cleaners, some non-alcoholic foods, etc, etc. All of these things cause an elevated reading that has nothing to do with alcohol consumption. The concentration of these chemicals varies in the different areas of the lungs, also. That's why the person running the test wants you to take a deep breath and then starts hollering "Breathe it all out!" and such stuff. They want to measure the very last part of the breath (from the bottom of the lungs), which can give a reading 50% above the first part. All of this is ignoring the issue of whether the equipment is actually working as it's supposed to, the physiological assumptions made to do the estimate (which, interestingly, generally discriminate against women), etc. If you're sure you're really not over the limit, then you're better off with a blood test to determine blood alcohol content, although police departments aren't noted for keeping that equipment clean and in proper working condition, either.