Three consolidated cases asked whether the Fourth Amendment permits warrantless blood or breath testing of drivers suspected of operating under the influence and whether a State may criminalize refusal to submit to such testing. The Supreme Court held that the Fourth Amendment permits warrantless breath tests incident to lawful drunk-driving arrests because the intrusion is limited and the government’s need for reliable evidence is substantial. Blood tests are materially more intrusive and generally require a warrant or a recognized exception. The Court also held that a State may not impose a crime for refusing a warrantless blood draw, although ordinary consequences for refusing a validly requested test may remain available. The Court reversed one judgment, affirmed one, and vacated and remanded another for reconsideration of whether consent was voluntary under the proper legal standard. Separate opinions disagreed about the scope of the search-incident-to-arrest doctrine and the practical consequences of the decision.