by Tsu Dho Nimh

Created on: December 14, 2008   Last Updated: March 17, 2012

If you blow a blood alcohol above the legal limit, a DUI citation is understandable. But what if you are under the legal blood alcohol limit and the arresting officer writes a DUI citation anyway. What do they use to decide whether you are impaired? Are you going to get convicted?

Although they are accurate, and when properly used give results that agree well with the blood tests for alcohol, a Breathalyzer machine is only as good as its operator, the operator's technique, and the machine's last calibration. Some brands are susceptible to temperature changes, and some may confuse the ketones found in the breath of some diabetics and dieters with alcohol.

A second factor is that Breathalyzers are most accurate if you are breathing normally; their design assumes normal breathing. Panting or hyperventilating can lower the apparent alcohol levels. Holding your breath briefly before the test or exhaling more air than necessary can elevate the results.

The so-called "roadside sobriety tests" may be used by police to decide whether to take you to the Breathalyzer testing station, or whether to issue a DUI citation despite the Breathalyzer results. If you failed the sobriety tests and passed the Breathalyzer tests, they may be confident enough in the roadside tests to issue a citation. The tests rely on coordination or other physical signs to judge impairment.

The heel to toe walking test, also known as "walk the line", has you walk 9 steps along a line, then turn and return along the same line. The heel must be placed directly in front of the toe of the other foot. You are judged on your ability to follow the instructions, how well you keep your balance, if you have to stop and regain balance, and if you are flapping your arms to try to maintain balance.

For the stand on one foot test, you are asked to stand on one foot with the other foot raised about six inches, then count out loud "one thousand one, one thousand two, etc." until asked to stop. The standard time is 30 seconds.
Either of these tests will be affected by any factor that affects your balance or concentration, such as the surface you are walking on, the weather, your normal physical coordination, current or past injuries to the feet and legs, illness, and some prescription or over the counter drugs. A very common cause of failure is the normal lack of balance that comes with allergies or upper respiratory infections that cause the inner ear to become clogged.

For the eye test (horizontal nystagmus test),

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