All drivers in California suspected of DUI are subject to the "implied consent" law once taken into custody.  That law, found in Vehicle Code section 23612, provides that the police may take a sample of an arrested driver's blood, breath or urine to test for blood alcohol content without asking permission.

Why Implied Consent? 

Each person has Constitutional rights to privacy and against self-incrimination.  Those Constitutional rights would be violated if the police took chemical samples from citizens without permission or consent.  Therefore, the law says that the act of driving a vehicle in California constitutes the consent that police need in order to take and test blood, breath or urine from an arrested DUI suspect.  Because that consent need not be given expressly, it’s called “implied consent.”

Consent to Alcohol Tests

Section 23612(a) permits the police to test either your blood or your breath if they suspect you’ve driven while under the influence of alcohol.  You get your choice from among the tests available.  If neither blood or breathalyzer test is available, you may be required to submit to a urine test.

Consent to Drug Tests 

Section 23612(b) permits the police to test either your blood or urine if they suspect you of driving under the influence of drugs other than alcohol.  

Your Options 

If in custody, you have the right to select the chemical test method among those made available; but you do not have the right to refuse all such tests.  In fact, your refusal of all chemical tests is itself a violation of law that can lead to enhanced penalties if convicted of DUI.  Also, your refusal to submit to a chemical test allows the DMV to suspend your license without a hearing.

Note that the "implied consent" law applies only after you are taken into custody.  It does not apply to the roadside PAS breathalyzer test, which the driver may refuse if over 21.