The U.S. Supreme Court ruled today that police don't need a search warrant before they open your mouth and take a swab of DNA if you've been arrested for a "serious crime."

The Supreme Court ruled in a 5-4 decision that DNA swabs are a "legitimate police booking procedure" that is allowed under the Constitution just like fingerprinting and mugshots.

The court's swing voter Justice Anthony Kennedy wrote the majority opinion, which said DNA identification has become an important tool to help police identify suspects.

Justice Antonin Scalia, one of the court's most outspoken conservatives, wrote the dissenting opinion that was joined by three of the court's liberal justices. Scalia's dissent questioned Kennedy's assertion that DNA helps police identify suspects.

"The court's assertion that DNA is being taken, not to solve crimes, but to identify those in the state's custody taxes the credulity of the credulous," Scalia writes in his dissent.

The Supreme Court's decision upholds a Maryland law that was challenged by Alonzo King, whose DNA was taken after he was arrested for pointing a gun at a group of people. Police matched his DNA to a rape that had gone unsolved for six years.

King was convicted of the rape and was given a life prison sentence.