Abreathalyzer is a device for estimating blood alcohol content from exhaled air. Any alcohol that a person drinks is absorbed from the mouth, throat, stomach, and intestines. The alcohol is not digested but remains in the blood and is then carried to the alveoli for gas exchange. Because of the volatility of alcohol, it evaporates and is exhaled. There is a direct relationship between alcohol concentration in the alveoli and alcohol concentration in the blood.