In the 2015 case Birchfield v. North Dakota, the U.S Supreme Court ruled on three consolidated cases involving state laws that criminalized a driver's refusal to submit to a blood or breath test in suspected drunk driving incidents. The court held that while warrantless breath tests are permissible under the Fourth Amendment’s search incident to arrest doctrine, warrantless blood tests are not. Breath tests do not implicate significant privacy concerns beyond arrest itself and provide necessary information for law enforcement officers dealing with intoxicated drivers. Blood tests, however, involve piercing of skin and extraction of part of subject's body thus implicating more serious privacy interests which require obtaining a warrant unless there is an emergency situation preventing it.

In the dissenting opinion for Birchfield v. North Dakota, Justice Sonia Sotomayor, joined by Justice Ruth Bader Ginsburg in part, argued that both breath and blood tests constitute a search under the Fourth Amendment. They contended that these searches should not be exempt from warrant requirements just because they serve a law enforcement need. The justices expressed concern over normalizing warrantless searches and eroding constitutional protections against unreasonable searches and seizures. They also disagreed with the majority's distinction between breath tests (which they found less intrusive) and blood tests (more intrusive), arguing this differentiation is inconsistent with privacy expectations protected by the Fourth Amendment.