Generally, in DUIs, the most significant piece of evidence is the breath or blood sample. That’s because, when determining guilt, nothing is more persuasive than blood alcohol content (BAC).


You are required to submit to a breath or blood test after you’re arrested. This is different than the preliminary (PAS) breath test during field sobriety tests before you are arrested, which is voluntary. Driving is considered a privilege, not a right. In California, that privilege is conditioned upon you consenting to provide a breath or blood sample if arrested for DUI. It’s called “implied” or “advance” consent.


If you refuse to provide a breath or blood sample, law enforcement generally cannot force you. Historically, forced blood draws were permitted. But, in 2013, the United States Supreme Court in Missouri v. McNeely changed the law. Now, if you refuse to take a test, officers must get a search warrant to force a blood draw. If not, they violate the Fourth Amendment’s prohibition against unreasonable searches and seizures. As a practical matter, getting a judge to sign a warrant on short notice, and most often late at night, may present challenges for law enforcement. However, warrants for blood draws are increasingly occurring as law enforcement agencies take steps to address that challenge.


All said, refusing to provide a breath or blood sample is certainly not without consequence. The DMV will automatically suspend your license for at least one year with no recourse to apply for a special license to allow you to drive to work. If you’ve refused the test in the past, then your suspension will be at least two years. Additionally, if prosecuted for DUI, the prosecutor will likely charge an “enhancement” allegation for your refusal, which generally will increase your punishment if convicted. But even with these added consequences, there are folks who’d still refuse to submit to a test. They would rather face these other consequences than allow their BAC to be known.

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