How Breathalyzers Work

Types of Devices: Intoxilyzer
Diagram of the Intoxilyzer
Diagram of the Intoxilyzer

­This device uses infrared (IR) spectroscopy, which identifies molecules ba­sed on the way they absorb IR light.

Molecules are constantly vibrating, and these vibrations change when the molecules absorb IR light. The changes in vibration include the bending and stretching of various bonds. Each type of bond within a molecule absorbs IR at different wavelengths. So, to identify ethanol in a sample, you have to look at the wavelengths of the bonds in ethanol (C-O, O-H, C-H, C-C) and measure the absorption of IR light. The absorbed wavelengths help to identify the substance as ethanol, and the amount of IR absorption tells you how much ethanol is there.

Diagram of the Intoxilyzer

In the Intoxilyzer:

  1. A lamp generates a broadband (multiple-wavelength) IR beam.
  2. The broadband IR beam passes through the sample chamber and is focused by a lens onto a spinning filter wheel.
  3. The filter wheel contains narrow band filters specific for the wavelengths of the bonds in ethanol. The light passing through each filter is detected by the photocell, where it is converted to an electrical pulse.
  4. The electrical pulse is relayed to the microprocessor, which interprets the pulses and calculates the BAC based on the absorption of infrared light.