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Are breathalizers accurate?

A breathalyzer is a device for estimating blood alcohol content (BAC) from a breath sample, or "Breathalyzer" is the brand name of a series of models made by one manufacturer of these instruments, but has become a genericized trademark for all such instruments. Intoxilyzer, Intoximeter, AlcoScan, Alcotest, AlcoSensor, Alcolizer, Datamaster are the other most common brand names in use today. The U.S. Government's National Highway Traffic Safety Administration maintains a "Conforming Products List" of breath alcohol devices approved for evidentiary use, as well as for preliminary screening use.

These instruments however are not without their ability for error. Breath testers can be very sensitive to temperature, for example, and will give false readings if not adjusted or recalibrated to account for ambient or surrounding air temperatures. The temperature of the subject is also very important.

Lastly one of the most common sources of error in breath alcohol analysis is simply testing the subject too early—while his or her body is still absorbing the alcohol. Absorption of alcohol continues for anywhere from 45 minutes to two hours after drinking or even longer. Peak absorption normally occurs within an hour; this can range from as little as 15 minutes to as much as two-and-a-half hours.

Failure of law enforcement officers to use the devices properly or of administrators to have the machines properly maintained and re-calibrated as required are particularly common sources of error. However, most states have very strict guidelines regarding officer training and instrument maintenance and calibration.