By WASHINGTON (CN) — The Supreme Court on Thursday struck down state laws that make it a crime for suspected drunken drivers to refuse a blood test.

Proving impairment usually requires testing of a driver's BAC, short for blood alcohol concentration, but many drivers are reluctant to submit to such tests voluntarily.

In the field of implied-consent laws that exist to overcome this obstacle, most states have a way to penalize noncompliant motorists.

Losing one's license has historically been the typical penalty, but North Dakota and Minnesota are among states that made a crime for motorists to refuse a test after they have been arrested for driving while impaired.

Back in December, the Supreme Court took up and consolidated three cases from these states to decide whether such laws violate the Fourth Amendment's prohibition against unreasonable searches.

William Bernard Jr., Steve Beylund and Daniel Birchfield each claimed that police should be required to obtain search warrant before demanding a test of their breath, blood or urine.

After detailing each man's exploits in today's 38-page lead opinion (pdf), Justice Samuel Alito said the drivers each seek similar relief despite the differences in their cases.

North Dakota police tried to force blood tests on Birchfield and Beylund, but Minnesota police informed Bernard that he had to submit to a breath test.

"Birchfield and Bernard each refused to undergo a test and was convicted of a crime for his refusal," the ruling states. "Beylund complied with the demand for a blood sample, and his license was then suspended in an administrative proceeding based on test results that revealed a very high blood alcohol level."

Alito dispatched with the issue of breath tests first, saying they neither implicate significant privacy concerns nor pose significant intrusions.

"Having assessed the effect of BAC tests on privacy interests and the need for such tests, we conclude that the Fourth Amendment permits warrantless breath tests incident to arrests for drunk driving," Alito wrote. "The impact of breath tests on privacy is slight, and the need for BAC testing is great.

"We reach a different conclusion with respect to blood tests," the decision continues. "Blood 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. Respondents have offered no satisfactory justification for demanding the more intrusive alternative without a warrant."

With breath tests widely deemed valid, Alito asked what justification states could have for warrantless blood tests.

"It is true that a blood test, unlike a breath test, may be administered to a person who is unconscious (perhaps as a result of a crash) or who is unable to do what is needed to take a breath test due to profound intoxication or injuries," the ruling states (parentheses in original). "But we have no reason to believe that such situations are common in drunk-driving arrests, and when they arise, the police may apply for a warrant if need be."

Alito scoffed at the notion that states have a basis to impose criminal penalties when drivers refuse to submit to invasive blood tests.

"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 justice wrote.

Alito added: "we conclude that motorists cannot be deemed to have consented to submit to a blood test on pain of committing a criminal offense."

For the three drivers, the court's holding today has different practical effects.

Bernard, the Minnesota driver who was prosecuted for refusing a breath test, will not see relief since he did not face an improper blood draw.

Birchfield was threatened with an unlawful search of his blood, however, so Alito said the judgment affirming his conviction must be reversed.

Beylund meanwhile submitted to a blood test because the police told him he had no choice.

Since Beylund's consent hinged on an erroneous assumption, Alito said the state court in North Dakota must re-evaluate Beylund's consent on remand.

Chief Justice John Roberts joined the lead opinion in full, as did Justices Anthony Kennedy, Stephen Breyer and Elena Kagan.

The remaining justices each partially dissented.

For Justice Sonia Sotomayor, the court should also require warrants for breath tests.

"A citizen's Fourth Amendment right to be free from 'unreasonable searches' does not disappear upon arrest," said Sotomayor, joined by Justice Ruth Bader Ginsburg. "Police officers may want to conduct a range of searches after placing a person under arrest. They may want to pat the arrestee down, search her pockets and purse, peek inside her wallet, scroll through her cellphone, examine her car or dwelling, swab her cheeks, or take blood and breath samples to determine her level of intoxication. But an officer is not authorized to conduct all of these searches simply because he has arrested someone. Each search must be separately analyzed to determine its reasonableness."

Sotomayor dispensed with the "common misconception" that breathalyzers are performed roadside at the time of the arrest.

In reality, getting the equipment ready, and escorting the driver to said equipment are just two of the hurdles.

The law also requires officers to wait 15 to 20 minutes for "residual mouth alcohol" to wear off. With time for the driver to contact their attorney, "nearly all breath tests 'involve a time lag of 45 minutes to two hours," according to the court record.

Sotomayor said this built-in window gives police plenty of time to seek warrants.

Finding the use of resources negligible, Sotomayor emphasized that states would be obtaining warrants only for those drivers who refused testing.

"A significant majority of drivers voluntarily consent to breath tests, even in states without criminal penalties for refusal," the opinion states. "Including States that impose only civil penalties for refusal, the average refusal rate is slightly higher at 24 percent."

Sotomayor slammed the majority for creating a "categorical exception to the warrant requirement because each of a state's judges and magistrate judges would need to issue less than one extra warrant a week."

Justice Clarence Thomas meanwhile dissented against the court's other finding.

"Both searches contemplated by the state laws at issue in these cases would be constitutional under the exigent-circumstances exception to the warrant requirement," Thomas wrote.

To Learn More:

Birchfield v. North Dakota (U.S. Supreme Court) (pdf)

Tests Used in 6 States to Identify Marijuana-Impaired Drivers Called Unscientific by AAA (by Joan Lowy, Associated Press)

LAPD to Ring in the New Year with Drug Tests at DUI Checkpoints (by Ken Broder, AllGov California)

How Often are Law Enforcement Officers Drunk on the Job? (by Matt Bewig, AllGov)

Texas Drivers Forced Off Road by Police to “Voluntarily” Give DNA Samples for Government Study (by Danny Biederman and Noel Brinkerhoff, AllGov)

Georgia Legislator Who Wants Welfare Recipients Drug Tested is Arrested for Drunk Driving (by David Wallechinsky and Noel Brinkerhoff, AllGov)