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How is breath testing done?

Police perform breath alcohol testing on a machine named Intoxilyzer 5000 EN. These devices are old and will soon be replaced. When new, sometime in the late ’90s, they cost approximately $7,500. According to the manufacturer, the device works on the basis of infrared light absorption by alcohol detected in a person’s breath.

According to the manufacturer and the Texas Department of Public Safety (DPS), the device subtracts the amount of light absorbed from the person’s breath sample, compares that amount with the amount of light originally introduced by the device into its testing chamber, and prints the difference as a test result.