From a Breath Sample to an Electrical Signal
A fuel-cell breathalyzer treats ethanol as a fuel in a tiny electrochemical reaction. When a person blows into the instrument, a measured portion of breath reaches an electrode coated with platinum. The platinum helps ethanol react with oxygen. In the process, ethanol molecules give up electrons; those electrons flow through an electrical path to the other electrode, creating a measurable current.
The instrument does not count alcohol molecules one by one. It measures the current produced during the test. Under the device’s designed conditions, more ethanol in the sample produces a stronger signal, so the electronics convert that signal into an estimate of the alcohol concentration in the breath.
Why Breath Can Estimate Blood Alcohol
Alcohol moves between blood and air in the lungs. In the small air sacs where gas exchange takes place, ethanol in the blood can enter the air that is breathed out. A breath sample therefore carries information about alcohol in the bloodstream, though it is not blood itself. The device applies a calibrated relationship between breath alcohol and blood alcohol concentration to report an estimate.
That chain matters: the displayed result depends both on the chemical signal and on how the instrument turns breath alcohol into a blood-alcohol estimate. The fuel cell measures ethanol in breath; the reported blood concentration is an inference built from that measurement.
