Understanding Breathalyzer Tests

A breath alcohol testing device estimates blood alcohol content by calculating the percentage of alcohol exhaled from the lungs. If the blood alcohol measurement is .08 or above, in a field breathalyzer test, a police officer in South Carolina has enough probable cause to make a drunk driving arrest. If blood alcohol measures .08 or higher at an approved breath testing site, you can be charged with driving under the influence (DUI). See the complete listing of DUI penalties according to blood alcohol levels.

How Can a Breathalyzer Measure Blood Alcohol?

The blood releases alcohol through the breath. When you drink alcohol, the body absorbs it quite literally. It saturates tissue lining in the mouth, throat, stomach and intestines, and enters the bloodstream. When that blood circulates through the lungs, alcohol evaporates out through air sacs in the lungs. A breathalyzer measures the alcohol in the breath that is exhaled.

There’s a mathematical relationship between alcohol blood level and alcohol breath level. It was determined that the alcohol measured in the breath can tell you something about the overall alcohol content in the bloodstream. A “universal” relationship was determined between the two levels alcohol concentrations (despite the fact that each person is unique). The golden rule of breath testing says: Every 2,100 ml of air in the lungs (breath to be exhaled) will contain the same amount of alcohol concentration as 1 ml of blood.

A device that can measure alcohol in the breath, can then estimate alcohol in the blood. Breath testing devices use special technology to calculate the amount of air expelled, the amount of alcohol in that air and then calculate a blood alcohol level based on the ratio above. In South Carolina, the only permissible breath testing device is the Datamaster (DMT), which uses infrared technology to measure the alcohol content in the breath.

Are Breathalyzer Tests Admissible in Court?

Results of handheld breathalyzer tests may be used to establish probable cause or reasonable suspicion of drunk driving. This allows a police officer to make an initial arrest and bring you in for an admissible breath test or blood test.

Results from the BAC Datamaster, a desktop breath testing device, are admissable as evidence in a driving under the influence charge if proper protocol for administering a breath test was followed, and you were advised of your breathalyzer rights and the law of implied consent.

If protocol was not followed, then your DUI criminal defense lawyer at Strom can challenge your breathalyzer test, among other infractions.

Hire a DUI Lawyer to Challenge Your Breathalyzer Test

Criminal defense lawyers at the Strom Law Firm, LLC provide a free consultation to discuss the facts of a DUI case. Founded by a former U.S. Attorney, the team at Strom Law also includes a former Public Defender, and a former Assistant Attorney General and Richland County Assistant Solicitor. It’s awarded the highest Martindale-Hubble ranking and collectively holds more than 50 years of complex litigation experience.


  1. […] Field sobriety tests (FSTs) were created to help law enforcement gauge the relative sobriety or intoxication of a driver, and cannot be used to determine blood alcohol level. However, a police officer who has pulled a suspicious motorist or who is working a sobriety checkpoint can request a battery of field sobriety tests which will likely then provide the officer with probable cause for an arrest and the use of an evidentiary alcohol test. […]

  2. […] you are pulled over for a suspected DUI, you may be subjected to a field sobriety test or a Breathalyzer test. These tests must be videotaped by the police officer, and the officer must inform you of […]

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