A breathalyzer (a portmanteau of breath and analyzer) is a device for estimating blood alcohol content (BAC) from a breath sample. "Breathalyzer" is the brand name of a series of models made by one manufacturer of these instruments (originally Smith and Wesson, later it was sold to National Draeger), but has become a generalized trademark for all such instruments. In Canada, a preliminary non-evidentiary screening device can be approved by Parliament as an approved screening device and an evidentiary breath instrument can be similarly designated as an approved instrument. The U.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.
Most handheld breathalyzers use a silicon oxide sensor to determine the blood alcohol concentration. Without proper software calibration, the accuracy of these sensors degrades over time and with repeated use. The calibration process aims to focus the sensor's ability to detect an accurate reading. New advances in breathalyzer design allow some models to self-calibrate or easily replace the sensor module without the need to send the unit to a calibration lab.