A Breathalyzer is an instrument used to estimate the BAC from someone's breath sample. Breathalyzer was originally a brand name but has now become the generic name for all devices of that nature. In Canada, Parliament can designate a preliminary non-evidentiary screening device as an approved screening device and an evidentiary breath instrument can be declared an approved screening instrument. Law enforcement officials most commonly administer Breathalyzer tests with portable roadside units that are now considered to be reliable enough to be admitted as evidence in DUI cases, while other agencies have shifted to larger and somewhat more accurate Breathalyzer machines.
Road side screening devices have developed greatly since the first roadside devices were used by police in the late 1930's. It was called the Drunkometer and it measured alcohol levels by having the motorist blow into a balloon inside the machine, running their breath through a solution and the greener the solution turned the more alcohol that was present. The current Breathalyzer provides law enforcement with a method for providing immediate results to determine an individual's BAC at the time of testing. It does not determine a person's level of intoxication as that depends on their tolerance to alcohol. When using a Breathalyzer the BAC test result can also be different between individuals consuming the same amount of alcohol because of factors such as genetic pre-disposition, weight and gender. With these improvements in technology test results from Breathalyzer's have become the most common and influential evidence in drunk driving cases.
A Breathalyzer cannot openly measure the concentration of alcohol in a person's blood (that can only be done with a blood sample analysis). They are only an estimate of a person's BAC based on measuring the amount of alcohol in someone's breath. As such they are open to error. A common issuing causing error in Breathalyzer testing as that they can be very sensitive to temperature and will give false readings if not adjusted or recalibrated to account for the direct and surrounding air temperatures as well as the temperature of the individual whose breath sample is being taking. Another issue is that the breathing pattern (or how out of breath the subject is) can also considerably change the results of a Breathalyzer test. One study found that there was a "15% decrease in BAC readings after vigorous exercise or hyperventilation. Hyperventilation for 20 seconds has been shown to lower the reading by approximately 32%." Inversely, holding your breath for 30 seconds can increase the breath test result by about 28% proving that a breath test is not the most accurate way to measure Blood Alcohol Content. A different study showed that the "BAC readings of subjects decreased 11 to 14% after running up one flight of stairs and 22-25% after doing so twice."
Breathalyzer's also encounter errors when they identify not only ethyl alcohol, but also any other methyl group compound. What this means is that a Breathalyzer can misinterpret other substances in human breath as alcohol content. Some machines have been confused in the past by the presence of acetone, which may be present in unusually high amounts in diabetics and other people with special dietary needs. Fumes from some paints, plastics and adhesives have also been known to produce false positive results in a not having the devices properly maintained and re-calibrated as required by temperature and use are the most common reasons an error or false reading can happen when a Breathalyzer test is preformed. The bottom line is that Breathalyzer's are not always accurate. That means if you've been charged with DUI and submitted a breath test you may still be able to challenge your result. See the information on DUI lawyers in your area if you are interest in learning more on challenging the results of a Breathalyzer test.