When you are pulled over because a law enforcement officer has reason to believe that you are driving after drinking, things usually move pretty quickly. At some point during the stop, you might be asked to take a field sobriety test. You might also be asked to take a breath test to determine your blood alcohol concentration. You have the right to refuse that breath test, but that refusal can trigger a different chain of events.
If you don't want to take a breath test and refuse, you risk your license being suspended. It is also possible for the law enforcement officer to get a blood sample to test to determine your BAC. Some counties in Missouri already have a policy that a search warrant must be obtained to get a blood test. A new ruling from the United States Supreme Court says that a search warrant is now required for all blood tests to check BAC.