States can criminalize refusal to take a breath test without a warrant after an arrest for drunk driving, because a breath test is categorically a search incident to arrest, the U.S. Supreme Court held June 23 in Birchfield v. North Dakota.

But States cannot criminalize refusal to submit to a blood test without a warrant, due to the blood test’s more intrusive nature, the Court held.


Three defendants were arrested for drunk driving, and refused either breath or blood tests.  They were convicted under laws in North Dakota or Minnesota which made such refusals misdemeanors or felonies.

They contended that the refusal laws violated the Fourth Amendment’s prohibition against unreasonable searches.


But the Court disagreed with regard to the breath tests, in an opinion joined in result by six justices.

As a general rule, a motorist cannot be compelled to submit to a warrantless search, the Court said. 

“If, on the other hand, such warrantless searches comport with the Fourth Amendment, it follows that a State may criminalize the refusal to comply with a demand to submit to the required testing, just as a State may make it a crime for a person to obstruct the execution of a valid search warrant,” the Court explained.

The Court examined the issue under the search-incident-to-arrest doctrine.  This requires balancing the degree to which the searches intrude upon an individual’s privacy with the government’s legitimate interests in preventing drunk driving, the Court said.

Breath test do not implicate significant privacy concerns, the Court found.  This is because they are minimally intrusive and do not pierce the skin.  They also reveal only one piece of information about a driver – the amount of alcohol in their blood. 
But “[b]lood tests are a different matter,” the Court said.  “They require piercing the skin and extracting a part of the subject’s body. … In addition, a blood test, unlike a breath test, places in the hands of law enforcement authorities a sample that can be preserved and from which it is possible to extract information beyond a simple BAC reading.”

In Missouri v. McNeely (2013), the Court held that blood tests require a warrant absent exigent circumstances, which generally must be something more than the natural dissipation of alcohol from the bloodstream.  The exigent circumstances exception to the warrant requirement “always requires case-by-case determinations,” the Court said.

Unlike McNeely, which examined the exigent circumstances exception, the issues in Birchfield depend on the search-incident-to-arrest doctrine.  That doctrine makes breath tests categorically permissible as a search incident to arrest for drunk driving, the Court said.  A case-by-case determination is not required for a search incident to arrest.   

But “[b]lood tests are significantly more intrusive, and their reasonableness must be judged in light of the availability of the less invasive alternative of a breath test,” the Court said.  The prosecutors here “offered no satisfactory justification for demanding the more intrusive alternative without a warrant.”

Nor can warrantless blood tests be justified by implied-consent laws, the Court said.  While the Court has approved civil penalties for refusals under implied-consent laws, imposing criminal penalties for refusal of intrusive blood tests “is another matter,” the Court said.  “There must be a limit to the consequences to which motorists may be deemed to have consented by virtue of a decision to drive on public roads.” 

The majority recognized that blood tests may be useful for detecting drugs in a driver’s blood that cannot be detected with a breath test.  “Nothing prevents the police from seeking a warrant for a blood test when there is sufficient time to do so in the particular circumstances or from relying on the exigent circumstances exception to the warrant requirement when there is not,” the Court said.


Justices Sotomayor and Ginsburg concurred with the majority concerning blood tests, but dissented from the Court’s ruling regarding breath tests. 

They would require a warrant for a breath test, unless exigent circumstances exist in a particular case.  “[A]llowing a categorical exception to the warrant requirement is a ‘considerable overgeneralization,’” they said.  They worried the Court was making the Fourth Amendment’s warrant requirement into “nothing more than a suggestion.”

Justice Thomas would allow warrantless searches of both breath and blood under the exigent circumstances exception.  Although he concurred in the result regarding breath tests, he said the majority “contorts the search incident to arrest exception” to reach a bad “compromise.”