Not Accurate!

The portable breathalyzer, which is used on the roadside, as well as the somewhat more sophisticated breath-test machine at the police station, are both subject to error. For the most part, both of these devices have the same weakness because they both work the same basic way—by measuring the alcohol content of the breath and using this measurement to estimate the alcohol content of the blood.

One of the most important factors that influence the results of both of these tests is breathing pattern. One study showed that holding your breath for 30 seconds before blowing into the breathalyzer increases the result a whopping 15.7 percent. Hyperventilating for 20 seconds, on the other hand, decreases it by 10.6 percent.

Yet another way in which breathing pattern can affect the results of a breathalyzer test has to do with what part of the breath the machine is exposed to. In other words, different parts of the exhalation will give different blood alcohol readings. The first part of the breath, made up of air from the top of your lungs, has much less alcohol in it that the last part of the breath, which comes from the bottom of the lungs.

Unfortunately, many police officers, knowing this, give the subject instructions like “Blow hard! Keep going!” Following these instructions will insure that the machine is exposed to the alcohol-rich blood from the bottom of your lungs. It is staggering to consider how many falsely high breathalyzer results have been obtained—and how many people have been arrested as a result—because of these instructions and the device’s potential for inaccuracy. Furthermore, these machines are not properly maintained.

No Penalty for Refusal of Roadside Breath Test:

There is no penalty for refusing to take the roadside breath test like there is for refusing the Breath Test or Blood Test at the police station or hospital. For this reason, many attorneys like Harrisonburg, VA DUI lawyer Bob Keefer advise all their clients to refuse the roadside breath test.


Bob Battle
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100% of my practice is devoted to serious traffic defense and criminal litigation in state and federal courts