In Florida, we have what is called implied consent which means that any person who obtains a driver's license in Florida consents to submit to an alcohol test where a police officer makes a valid stop and has probable cause to believe the person is driving under the influence of alcohol. This usually takes the form of a request by the police officer to blow into a breathalyzer at the jail after the person has been arrested for DUI. Whatever the reading is, the state will usually seek to use that evidence against the defendant in court in the DUI case. Where the breathalyzer reading is below the legal limit of 0.08, the police are not likely to unarrest the defendant, for lack of a better word.
A person who has been arrested for DUI can refuse the breathalyzer test. The police will not force a person to blow into the breathalyzer to get a breathalyzer result. In some cases, the police officer can request a test of his/her blood rather than a test of his/her breath. In a recent DUI case that went up to the United States Supreme Court, the DUI suspect refused to submit to a blood alcohol test and the police officer took his blood anyway to test it for alcohol content without a search warrant. The DUI case was appealed all the way to the Supreme Court.
The criminal defense lawyer argued that to take the defendant's blood was a search and seizure under the Constitution, and it was unreasonable without a search warrant signed by a judge. The state argued that there was an exception to the general rule that the police need a search warrant for a search and seizure. Generally, the state needs a search warrant to search someone, including taking their blood. However, there are exceptions to the search warrant requirement. If there are emergency circumstances, such as the risk of losing evidence if the search is delayed, the state may be able to conduct a search without a search warrant. In this DUI case, the state argued that the blood concentration dissipates as time goes by so the police officer needed to get the blood for alcohol testing as soon as possible.
The Supreme Court disagreed. They held that this argument was not sufficient to eliminate the search warrant requirement for blood in a DUI case. There are other circumstances where the state can take blood from a defendant in a DUI case, or test blood that was already taken by medical personnel, but in a standard DUI case where the DUI suspect refuses to give a blood sample, the police cannot force a blood sample without a proper search warrant.