For drivers 21 and older, the so-called legal limit refers to a blood alcohol concentration, or BAC, of 0.08%. When police pull over a driver on suspicion of drunk driving, they typically ask the person to perform a road sobriety test in which they must walk a straight line, stand on one leg and perform other simple acts of coordination or balance. After this, they often ask drivers to submit to a BAC test, usually through a chemical breath analysis device.
Under Wisconsin law, drivers are presumed to have implied their consent to a breath, blood or urine BAC test in advance, when they became licensed drivers in the state. Refusing the test can come with penalties in addition to any other penalties related to the drunk driving charges.
A person with a BAC of 0.08% or higher is legally considered too intoxicated to drive. The police will hand the BAC test results to prosecutors, who will use it as evidence against a defendant in a drunk driving trial.
A bad BAC test result can be very powerful evidence against a defendant, but it doesn't represent the end of the case. One common defense strategy for people accused of drunk driving is to question the dependability of the testing device.