If you are pulled over by the police while driving, and while speaking with them they smell alcohol on your breath, they will suspect that you are under the influence of alcohol. Based on this suspicion, the officer will ask you to perform a series of physical tests in an effort to determine if you are too drunk to drive safely. The first test that you will be asked to perform is to blow into the Preliminary Alcohol Screening Device. This is a small handheld device. The device will then register a number showing the percent of alcohol in your blood stream. The next test is the Horizontal Gaze Nystagmus Test. The officer will hold a pen in front of your face and move the pen from side to side. You will pass the test depending on how smoothly your eyes follow the pen. The next test is the Heel to Toe test. You will be asked to take 9 steps forward putting one foot in front of the other and touching the front of your foot to the heel of the other foot. You must not lose our balance during this test.The final test is the One Leg Stand. You will be asked to stand on one foot and count out loud for 30 seconds. Again you must not lose your balance on this test. If the office determines that you have passed all these tests than he or she will send you on your way. If the officer decides that you have not passed these tests then you will be arrested. That's why it's a good idea to have the name and phone number of an excellent San Francisco Criminal Lawyer in your wallet.