Police officers can test your BAC levels in a variety of ways. One of the most common ways is to use a breathalyzer test. They can also order a blood alcohol test, in which they will draw a blood sample, collect it in a test tube and send it off to a lab. Or, they can use a chart to determine your BAC levels.
Sometimes, police officers use field sobriety tests, which test a person's physical abilities, such as walking or balancing.