Being pulled over for suspicion of DUI can be a scary experience. In California, a police officer needs probable cause to believe you’re driving under the influence of alcohol or drugs in order to pull you over. However, if you’ve been pulled over for some other driving offense, and the officer suspects that you’ve been drinking or are impaired from drug use, they will ask you to submit to a breathalyzer test. You may later need to undergo a blood test as well because the breathalyzer only indicates blood alcohol content level (BAC) and not the presence of drugs in your system.