Can Police Force a BAC Test Without a Search Warrant?

A number of states in the U.S. have ‘implied consent’ laws that require drivers to submit to a BAC test. Failure to comply is considered proof of DWI guilt. Is this Constitutional? Are implied consent laws legal?  Can police legally force a BAC test without a search warrant?

The Fourth Amendment protects people from unreasonable searches by the government. But it’s only a guarantee against searches that are unreasonable under the law.

What is unreasonable? That results from balancing two conflicting interests. One is an intrusion on an individual’s rights. The other are government interests.

Courts decide specifically what is unreasonable. The Supreme Court has held that search warrants must be obtained under most circumstances before a search is conducted.

The Supreme Court has held that police can not routinely conduct BAC tests without a search warrant. Justice Sonia Sotomayor wrote for the Court.

In those drunk-driving investigations where police can reasonably obtain a warrant before a blood sample can be drawn without significantly undermining the efficacy of the search, the Fourth Amendment mandates that they do so.

BAC test without a search warrantThere are strong arguments on both sides of the issue. The case is expected to be argued soon. The Court will then determine whether implied consent laws are are Constitutional. It will also decide if  police can legally force a BAC test without a search warrant.

The Supreme Court’s decision could support the status quo. Or it could cause a major change in law enforcement procedures. Stay tuned.



Other News. Illinois Bev Guide, 2016, 16(3), 8.

What Does the Fourth Amendment Mean?


Alpert, R. DWI Investigation & Prosecution. Austin, TX: Texas District & County Attorneys Assn, 2005.

Keech, C., and Fairchild, C. Dude, What are My Rights? Kansas City, MO: Keechild, 2004.

Taylor, L., and Oberman, S. Drunk Driving Defense. Frederick, MD: Aspen, 7th ed., 2010.