In order for a Breathalyzer to be used by law enforcement the exact device must be on a list of approved devices compiled by the Department of Transportation. The current list authorizes approximately 40 different devices made by less than 20 different manufacturers located across the U.S. and around the world.

How have Breathalyzers improved over the years?

The original breathalyzer was a much cruder device and was nowhere near as portable as its more modern descendents. The first breathalyzer, developed in the 1930s, required the subject to blow a sample breath into a balloon, which captured the sample for later laboratory testing. For accurate results, breathalyzers needed a sample of the air from deep in your lungs, because this is where the various gasses in your body exchange between the lungs and the blood stream.
Since the goal is to measure the blood alcohol content (BAC) of the subject, in order to do this without actually measuring the blood itself the machine needs a deep breath; shallow breaths will not give accurate results. This is why you are required to blow into the device for a certain length of time and strength, to ensure the device captures the sample from deep in your lungs.

What other devices, if any, are available to test alcohol?

The main alternatives to BAT devices are field sobriety tests and urine or blood samples taken at the police station. The field sobriety tests are problematic because they can be subjective, and rely heavily on statement of the arresting officer. The urine or blood sample tests are problematic because they are not taken at the scene of crime, and if delayed too long, the amount could dissipate and the subject’s BAC could go down.

Are complaints about faulty breathalyzer results common?

There will always be complaints about the accuracy of these devices. Such challenges are a predictable and easy accusation to make when fighting a DUI/DWI conviction. The technology has advanced significantly, but it is not perfect, and the device can still be fooled as discussed below.

What are some common sources of error in breathalyzer testing?

Calibration errors are a big source of erroneous readings. BAT devices are very sensitive to surrounding conditions (i.e. temperature) and can often require specific recalibration for changes in climate. However, such recalibrations can go awry. For example, as of June 2010, approximately 400 drunk driving convictions were in question in Washington D.C. when it came to light that the devices used were improperly adjusted by city police.
Breathalyzers can also give false-positives if the alcohol levels of the mouth are tested instead of the blood, or there is a reaction to other innocuous chemicals in the subject’s blood.
In addition, since most tests are not administered directly after the subject is stopped by police, the prosecution will often hire experts to analyze the BAC level at the time of the test and extrapolate backward in time (i.e. make an educated guess) to judge what the subject’s BAC was at the time of the traffic stop.

Do I need a criminal defense attorney?

If you have been stopped for a DUI or DWI and had a Breathalyzer test administered, you should definitely speak with a DUI/DWI lawyer to see whether there are any possible reasons why the results aren’t accurate.