How do you test to see if someone has alcohol in their system?

There are two main ways to check someone’s blood-alcohol content:

  • Breathalyzer: As you drink, the alcohol goes through your bloodstream to your lungs. There, it evaporates into the lungs, and you breathe it out. As you blow into the breathalyzer, it can estimate your BAC by how much alcohol detects in your breath.
  • Blood test: A lab technician draws a small amount of blood with a needle. The technician then analyzes for the BAC. The blood test is most accurate within six to 12 hours after the last drink you consume.

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