Preliminary Breath Test vs. Official Post-Arrest "Chemical Test"
Generally, in DUI cases, 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").
After you are arrested, by law, you are required to submit to a "chemical test," which is your choice between breath or blood test. This is different than the preliminary alcohol screening ("PAS") device breath test, which is administered as a field sobriety test before you are arrested. The pre-arrest PAS test is voluntary, but the post-arrest chemical test is not. That's because driving is considered a privilege, not a right. In California, your driving privilege is conditioned upon you consenting to provide a breath or blood sample if ever arrested for DUI. The courts call this “implied” or “advance” consent.
What if you refuse the chemical test post-arrest?
If you refuse to provide a breath or blood sample, law enforcement generally cannot force a needle in you on the spot. 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 at times present a challenge for law enforcement. For the first few years following McNeely, agencies scrambled to get a system in place to address late night warrants. However, by now, most agencies have taken proper steps to address that challenge.
Even if you got lucky that a judge wasn't available to sign a warrant, 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.