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How Breathalyzers Work

Types of Devices: Alcosensor III or IV

­Moder­n fuel-cell technology (which may power our cars and even our houses some day) has been applied to breath-alcohol detectors. Devices like the Alcosensor III and IV use fuel cells.

The fuel cell has two platinum electrodes with a porous acid-electrolyte material sandwiched between them. As the exhaled air from the suspect flows past one side of the fuel cell, the platinum oxidizes any alcohol in the air to produce acetic acid, protons and electrons.

The electrons flow through a wire from the platinum electrode. The wire is connected to an electrical-current meter and to the platinum electrode on the other side. The protons move through the lower portion of the fuel cell and combine with oxygen and the electrons on the other side to form water. The more alcohol that becomes oxidized, the greater the electrical current. A microprocessor measures the electrical current and calculates the BAC.

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Operators of any breath alcohol testing device must be trained in the use and calibration of the device, especially if the results are to be used as evidence in DWI trials. Law enforcement officers can carry portable breath testing devices that use the same principle as full-size devices. Court cases can turn on the perceived accuracy of a breath test, however, so prosecutors rely on the results obtained from full-size devices.

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