How Long do Breathalyzers Detect Alcohol?

By Dyna Whiting ; Updated March 21, 2017

A breathalyzer is a standard device for measuring blood alcohol content, or BAC. The more you drink, the longer you need to wait for the alcohol to clear your bloodstream. On average, a serving of alcohol, like a bottle of beer or a glass of wine contains about one-third to one-half ounce of pure alcohol, and it takes about one hour for each serving to be eliminated from your body.

Blood Alcohol Level

Alcohol is absorbed into the body at a much quicker rate than food. On an empty stomach, 20 percent of alcohol is absorbed immediately into the bloodstream. Measured scientifically in milligrams and deciliters, the average person's body breaks down alcohol at a rate of 20 to 30mg/dL per hour. The standard rate of alcohol excretion is 0.015 blood alcohol content (BAC) points per hour. Breathalyzers use BAC to show the current measure of alcohol in your body via a breath analysis.


Alcohol is either metabolized by the body or excreted via breath, sweat or urine. Breathalyzers work by measuring the concentration of alcohol in the air exhaled by an individual. Alcohol concentration of the breath is at around a 2100:1 ratio in relation to the concentration in the blood. Breathalyzers utilize either electrochemical fuel cell sensors, semiconductor oxide sensors or infrared spectrophotometers to identify the alcohol content of an individual's breath and calculate it into a reading as a percentage of blood alcohol content.

Types of Breathalyzers

As mentioned earlier, there are three types of breathalyzers. Electrochemical fuel cell sensors are accurate in addition to being conveniently handheld. A fuel cell in the device measures alcohol levels through a chemical reaction that oxidizes the alcohol present and produces an electrical current. More alcohol equals a greater current and the readings are shown accordingly. Breathalyzers using infrared spectrophotometers, on the other hand, are large table-top devices that identify alcohol by the way light is absorbed by the breath sample being examined. These are often only found in research centers or at police stations, because of their size. Semiconductor oxide sensors are the most recent development in breathalyzer technology. They use an ethanol-specific sensor to measure BAC and are growing in popularity due to low costs, small size and extremely accurate readings.

Time Frame for BAC Detection

The length of time that breathalyzers are able to detect alcohol varies. For the most part, breathalyzers can detect even the smallest amount of alcohol in a person's system. However, the concern for most people is that their blood alcohol levels be under the legal limit for being considered intoxicated. In the U.S., an individual's BAC needs to be under 0.04 to pass a breathalyzer test while 0.08 is considered drunk. As mentioned earlier, 0.015 BAC is the standard rate that alcohol leaves the body. To determine the number of hours needed for your body to be free of alcohol, simply take a breathalyzer reading and divide it by the standard. For example, if a breathalyzer gave a BAC reading of 0.150, divide 0.150 by the standard 0.015, which will equal 10. This means that it will take 10 hours for the alcohol to clear your body.


Since they do not measure blood alcohol content directly, breathalyzers are prone to error. Various factors such as body temperature, blood composition, the presence of blood in the mouth or acid reflux can play a role in creating inaccurate readings. Also, there are many compounds found in the body, such as ketones, that are chemically similar to alcohol, and high levels of such compounds could produce a falsely high reading. Devices using semiconductor oxide sensors have proven to be the most accurate, with accuracy levels of ±0.01 percent at 0.10 percent BAC.

About the Author

Dyna Whiting has been writing and editing health, science and technology related material for nine years. A lot of her experience was established in producing articles and business documents for organizations that are not proficient in English. She holds a Bachelor of Arts in psychology with a pre-medical background.