Breathalyzers rely on an indirect measurement of blood alcohol concentration by estimating the amount of alcohol in a puff of exhaled breath. Although breathalyzers are possibly the most inaccurate chemical sobriety tests, they are also the most common.
The device is extremely versatile, lightweight, inexpensive, and accessible. Officers can keep the device in their car for immediate access in the event of a suspected drunk driving incident.
Officers are trained to operate breathalyzers on the scene. They are advised to perform a breathalyzer test only after no less than 20 minutes of careful observation. This amount of time and observation allows for sufficient reason to doubt sobriety. Officers must watch the driver to make sure that he or she has not vomited or burped before the test is given. The officer should also make note of any blood or open sores in the mouth.
The presence of vomit, blood, gas, or liquids in the mouth can significantly alter the results of a breathalyzer test. For instance, the alcohol level in vomit can nearly double the alcohol level in the sample of exhaled breath.
The officer must also monitor the subject’s breath and breathing pattern. False BAC readings can also result from an altered breathing rate due to vigorous exercise or from holding one’s breath.
If an officer administers the test early, without due warning or proper initial observation, or with an improperly maintained unit, he or she may get an inaccurate reading. Due to this obvious flaw, many state laws now require the officer to follow up a breathalyzer test with a more accurate breath analysis test at the station or with a blood or urine test. Some states have even banned the use of the onsite breathalyzer test, deeming the practice too unreliable.
Despite a long history of alcohol breath test development dating back to the 1930s, even today’s most advanced breathalyzer models are still prone to error that is human-related, maintenance-related, or due to an outside influence. Some of the outside influences that can alter breathalyzer test results include: