When you take a drink of an alcoholic beverage, the alcohol doesn't get digested the way food does. Instead, it passes directly into the bloodstream. When blood passes through your lungs to pick up oxygen, some of the alcohol vaporizes and leaves your body when you exhale. A breathalyzer device detects that alcohol and uses the percentage of alcohol in your breath to determine the percentage in your blood.
Types
There are three basic breathalyzer technologies: fuel cell, semiconductor oxide and spectrophotometer. The handheld breathalyzers commonly used by police in the field are either fuel cell or semiconductor oxide devices. A spectrophotometer breathalyzer is a tabletop unit; the police have to take you down to the station to test you on one of these. With all three types, the test starts with you blowing into the machine.
Fuel Cell
A fuel cell breathalyzer uses an electrode to break down the alcohol molecules in a breath sample into acetic acid, electrons and protons. This process creates an electric current; by measuring the strength of that current, the device can tell how much alcohol is in the sample. Fuel-cell breathalyzers are the more accurate and reliable of the two handheld types, according to KHN Solutions, a major breathalyzer manufacturer that produces both types of devices, and Breathalyzer Canada, that country's No. 1 seller of alcohol testing products.
Semiconductor Oxide
Inside a semiconductor oxide breathalyzer is a sensor made of tin dioxide. When alcohol molecules come into contact with the sensor, they change its electrical resistance. By measuring the difference in the resistance, the device calculates how much alcohol is in the breath sample. Semiconductor oxide devices aren't as accurate as fuel-cell versions, which is why they are geared more to the consumer market rather than police agencies. The advantage of these devices is that they're smaller and cheaper and consume less power.
Spectrophotometer
Breathalyzers that employ spectrophotometry work by measuring how the molecules in the breath sample absorb infrared light. Every molecule reacts to infrared light differently, so the device can determine the chemical makeup of the sample.
Fooling the Test
Breathalyzers measure alcohol coming from the lungs, not the stomach, so the contents of your stomach are irrelevant to the results. Also, all three types of breathalyzers look for alcohol's chemical signature. They don't work by smell, which is why tricks such as sucking on pennies, chewing gum or eating breath mints won't affect the results. These tactics, frequently offered up as ways to "fool" a breathalyzer, are urban legends, says researcher Barbara Mikkelson of Snopes.com.
