The "Implied Consent" laws of California provide that if you are arrested for drunk driving, you are presumed as a condition of the privilege to drive to have impliedly consented to chemical testing. If you refuse to submit to testing, your driving privilege can be suspended. The chemical test will normally consist of your choice of breath or blood analysis; a urine sample can be taken instead if neither breath nor blood are readily available.

What most people do not know, when they are in the middle of a DUI investigation, is that this test must be done after the arrest is made. An investigating officer will often times ask a DUI suspect to breathe into a portable breath testing device before he/she has actually been placed under arrest. This is known as a preliminary alcohol screening or "PAS" device. While the officer is supposed to tell you that this is an optional test, this point is often omitted, and the suspect is simply asked to blow into the device. The possible impending arrest for a DUI is a very scary thing and for many people it goes so quickly that they do not pause to ask if they have to do the things the officer is asking of them.

There are good reasons why you should not be tricked into agreeing to take the preliminary alcohol screening or "PAS" device, since if you breathe into this device and it detects any measurable BAC, this is all the probable cause an officer needs to place you under arrest.

On the other hand, if the officer has not observed any abnormal driving patterns, has not detected any of the normal signs of alcohol consumption or drug use, which include blood shot eyes, the presence of alcoholic containers or drug paraphernalia in the vehicle, slurred or difficult speech, fumbling or other physical signs of intoxication, admission of drug or alcohol use, or inconsistent responses to answers of questions, and you have refused to perform any FSTs, and you have not agreed to take the preliminary alcohol screening, the officer may lack the probable cause to make an arrest, which would make any subsequent arrest unlawful, which would result in your case being dismissed or charges never being filed by the district attorney in the first place.

However you must remember, while you are not required to breathe into a portable breath testing device before you are actually placed under arrest, under the California State implied consent law, you must provide a breath or blood sample after you have placed under arrest.

Any person who is arrested for DUI and subsequently refuses a chemical test (blood or breath) will still be charged with DUI, but will also be charged with a "refusal enhancement" as well. Statutorily, the refusal enhancement can increase the DUI penalties by imposing additional, and much more jail time on the person arrested.