Everyday Chemistry: The Fuel-Cell Breathalyzer 

• Breathalyzers work because the amount of ethyl alcohol in the breath is proportional to the amount of ethyl alcohol in the bloodstream. One type of breathalyzer is a fuel cell consisting of two platinum electrodes wired to a meter and some electrolyte.
• At the anode, ethyl alcohol in the breath is oxidized to acetic acid.
• At the cathode, oxygen is reduced.
• The amount of electrical current produced depends on the amount of alcohol in the breath.
• A higher current reveals a higher blood alcohol level. When calibrated correctly, the fuel-cell breathalyzer can precisely measure the blood alcohol level of a suspected drunk driver.