The police have three main methods of determining if you're driving under the influence of alcohol or drugs: observation of your driving behavior; chemical tests; and sobriety tests, such as walking a straight line or reciting a list of letters or numbers. The chemical tests are generally blood, breath or urine tests. Blood tests measure the amount of various substances in your blood, while breath or urine tests calculate the amount of substances in your system using a mathematical formula. In roadside sobriety checks, breath tests are a common and convenient method of establishing whether or not you're under the influence of alcohol or intoxicated. In most states, you're obliged to submit to these tests at the request of a police officer, and failure to do so can result in the immediate confiscation of your driver's license. Most states impose other penalties for refusing to take a breath test. In a few states, for example California, you don't have the right to an attorney before submitting to a breath test. In other states, you have the right to an attorney before taking any chemical tests. Generally speaking, if you're stopped by the police and asked to take a breath test, you should comply with the officer's request. Your refusal to submit to a breath test can provide a prosecutor with a damaging argument against you if you're charged with an alcohol-related offense and taken to court.