Alcohol stays on your breath for as long as it is in your bloodstream. Because the body removes alcohol at a fairly steady rate, a breathalyzer can usually detect it for several hours after your last drink, and after heavy drinking it can still be detected the next morning.
Why a breath test reflects your blood alcohol
As blood passes through the lungs, a small amount of the alcohol it carries moves into the air you breathe out. A breathalyzer measures the alcohol in that air and uses it to estimate your blood alcohol content (BAC). Fuel-cell (electrochemical) sensors, like the one in the i Alco Supreme, are the type most commonly used for accurate personal and professional testing.
How long alcohol can be detected
On average, the body lowers BAC by about 0.015% per hour. The table below shows roughly how long it takes to return to zero from different peak levels. These are estimates only, and the clock starts once alcohol has been fully absorbed, usually 30 to 90 minutes after the last drink.
| Peak BAC |
Approximate time to clear |
| 0.02% |
About 1 to 2 hours |
| 0.05% |
About 3 to 4 hours |
| 0.08% |
About 5 to 6 hours |
| 0.15% |
About 10 hours |
| 0.20% |
About 13 hours or more |
What affects how long alcohol stays on your breath
- How much you drank and how quickly you drank it.
- Whether you ate before or while drinking, since food slows absorption.
- Your body size, sex and body composition.
- Your personal elimination rate, which usually falls between 0.010% and 0.020% per hour.
Coffee, cold showers, exercise and sleep do not speed up how quickly your liver removes alcohol. Only time lowers your BAC.
Mouth alcohol and false positives
Alcohol that is still in your mouth, rather than in your blood, can cause a falsely high breath reading. Common sources include mouthwash, breath sprays, some cough syrups and medications, and very recent food or drinks that contain small amounts of alcohol.
Mouth alcohol usually disappears within about 15 minutes. That is why breath testing instructions generally recommend not eating, drinking, smoking or using mouthwash for 15 minutes before a test, and why a second test after a short wait is a common way to confirm an unexpected result.
Breath tests compared with other alcohol tests
A breath test shows whether alcohol is in your system right now, which makes it well suited to confirming sobriety at a specific time. Other tests look further back: urine tests for alcohol by-products such as EtG can detect drinking over the previous few days, and hair tests can show patterns over months, but neither shows whether someone is impaired at the moment of testing.
What this means for remote alcohol monitoring
Because alcohol is only detectable on the breath for a limited number of hours, the timing of tests matters as much as the number of tests. Spreading scheduled tests across waking hours and adding random tests makes it much harder for drinking to go unnoticed between tests.
With Druchol, tests can be scheduled at fixed times, generated randomly up to 4 times a day, or requested on demand, and every test is recorded on video with its location.
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