Intoxilyzer make use of a technique called infrared (IR) spectroscopy, This technique is capable of identifying molecules based on the fact that different molecules absorb IR light differently.

Molecules are constantly vibrating & when a molecule absorbs the IR light this vibration pattern changes. This change in vibration is due to change in bonds and bends/stretching of the bonds.

Each bond with in the molecule absorbs different wavelength of the OR light. The wavelength absorbed allows the detection of the molecule type and amount of IR absorption determines the amount of molecule present.