How Long Does a Breathalyzer Detect Alcohol?

Feb 15, 2017

Used by law enforcement and in ignition interlock devices, breathalyzers have become the primary tool for detecting the presence of alcohol and measuring a person’s blood alcohol concentration when taking a blood or urine sample may be too difficult at that moment in time.

They can be an impactful tool in discouraging and preventing alcohol-impaired driving and any injuries, deaths, or property damage resulting from it. Many people wonder how long car breathalyzers can detect alcohol on your breath. Read on to learn more on how ignition interlock devices work.

Breathalyzers and BAC

Breathalyzers work by measuring your blood alcohol concentration, which is expressed as a percentage that equates to the weight of ethanol in grams for every 100 milliliters of blood. For example, a BAC of 0.08 means 0.08 grams of alcohol per 100 milliliters of blood.

But how can breathalyzers determine your blood alcohol concentration through your breath? When you drink an alcoholic beverage, the alcohol does not get broken down immediately, and it enters your bloodstream without any real changes to its chemical structure. This allows the substance to flow throughout your body along with your blood.

As your blood passes over your lungs, some of the alcohol evaporates into tiny air sacs in the lungs known as alveoli. The alcohol in the alveoli is detectable through every exhale and is directly related to the concentration of alcohol in your blood at a ratio of 2,100 to 1. That means that 2,100 milliliters of air you exhale contains as much alcohol as 1 milliliter of your blood.

Breathalyzers work in various mechanisms to measure the alcohol in your alveolar air and calculate it into a BAC.

How Long Can a Breathalyzer Test Detect Alcohol On Your Breath?

So then, how long after drinking can you use an Ignition Interlock? It’s important to understand that you cannot “beat” a breathalyzer. Breathalyzers are highly accurate and reliable given regular maintenance and calibration, both of which are required if you use a car breathalyzer. Really, the question of how long a breathalyzer can detect alcohol comes down to how you metabolize alcohol.

Once alcohol enters your body and bloodstream, it can only exit through two means. About 10 percent leaves through your urine, breath, and sweat. The other 90 percent is metabolized naturally in the body. The rate of metabolism can differ based on a wide range of factors, but experts generally agree that it takes one hour to break down 0.015 of blood alcohol concentration, meaning that for every hour that you are not drinking, your BAC will go down by 0.015.

One standard drink (which is considered any drink containing 14 grams of alcohol) will increase your BAC by a maximum of 0.02, based on your body size, gender, and other factors. Within about an hour, your blood alcohol concentration would be at almost zero. The problem usually comes when you drink at a faster rate or otherwise drink several alcoholic drinks at once (like taking several shots). Your liver cannot process alcohol that quickly, causing it to accumulate in your blood and leading to a higher BAC. For the average person, it only takes about three or four drinks in one hour to reach a BAC of 0.08.

Given the general rule, if your blood alcohol content is at the limit of 0.08, it would go down to 0.065 after one hour. It would take roughly five hours and twenty minutes for your body to completely metabolize the alcohol and eliminate it from the body. That’s also why it can be dangerous to drink too late into the night. If you have a high enough BAC, you may still actually be drunk when you wake up, which can still be a real problem if you have to drive to work. Those who have been binge drinking can have alcohol in their systems for over 10 hours.

Breathalyzers can detect alcohol within 15 minutes of your first drink and can continue for as long as the alcohol is in your system. Coffee, cold showers, and “sleeping it off” will not sober you up. Time is the only thing that can lower your BAC, so be smart about your drinking and always have a backup plan to get home.

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