Breathalyzer

A device that estimates blood alcohol concentration (BAC) from alcohol measured in exhaled breath. Its result is an indirect estimate, not a direct measurement of alcohol in blood.

Fuel cell sensor: An electrochemical sensor that produces an electrical current when a fuel is oxidized at an electrode. Many evidential breathalyzers oxidize ethanol in a fuel cell and infer its amount from the resulting current.
Preliminary breath test: A roadside breath test used to screen for possible alcohol impairment. Portable breathalyzers commonly provide this quick screening result before formal testing.
Blood alcohol test: A laboratory or point-of-care measurement of alcohol concentration in a blood sample. It measures alcohol in blood directly, unlike a breathalyzer's estimate from exhaled air.
Blood alcohol concentration: The concentration of ethanol in a person's blood, commonly expressed as grams per deciliter or a percentage. Breathalyzer readings are commonly reported as estimates of this underlying quantity.
Retrograde extrapolation: An estimate of an earlier blood alcohol concentration based on later measurements and assumptions about alcohol metabolism. Breath results taken after driving may be used in estimates whose timing and assumptions are contested.
Infrared spectroscopy: A method that identifies and measures substances by how they absorb infrared radiation. Some evidential devices detect ethanol through its characteristic infrared absorption.
Evidential breath testing: Breath testing performed under procedures intended to produce legally admissible alcohol measurements. Evidential instruments use stricter protocols and records than handheld screening devices.
Urine alcohol test: A test that measures alcohol or its metabolites in urine. Urine testing reflects alcohol excretion over time rather than breath alcohol at the moment of testing.
Per se intoxication: A legal rule making alcohol concentration above a specified limit sufficient to establish an offense. Breathalyzer evidence is often used to determine whether a driver exceeded a statutory BAC threshold.
Alcohol absorption: The movement of ingested ethanol from the digestive tract into the bloodstream. During absorption, blood and breath alcohol may not follow the steady relationship assumed by conversion methods.

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