To ensure innocent citizens are not arrested, most states, a police officer must have probable cause to believe someone is under the influence before he can require a person to submit to any form of blood alcohol concentration test.
For example, in Arizona, in order to prove probable cause, a police officer can use his subjective opinion and observations of erratic driving, slurred speech, odor, and can use a portable breathalyzer. Once a police officer has established probable cause, he can ask the driver to submit to a blood, urine or breath test either at a police station or a local hospital. A driver can refuse the test, but anyone who refuses the test may be assumed to be guilty under "implied consent" laws. One defense to a conviction based on a driver's refusal to take a blood alcohol concentration test is the fact that police officers did not make the consequences known to the driver who refuses the test.
Law enforcement may pull a driver over for changing speed erratically, going too fast or to too slow, an inability to stay inside the lines of a lane of traffic, failing to yield at stop signs, intersections, or stop lights or for aggressive driving.
Police officers often strike up a conversation immediately upon on any traffic stop to assess a driver's ability to carry on a conversation, maintain eye contact, etc. Police will be looking for signs of slurred speech, the smell of alcohol on a driver's breath, bloodshot eyes, or even the occasional comment by a driver that he is coming from a party or a bar.
The side of the road is no place for an argument with law enforcement and it's no place for you to start making legal arguments. Save your legal arguments for the court. You should be polite and know that you do NOT have to answer any questions without a lawyer present. You will obviously draw more suspicion to yourself if you are not respectful or if you do not answer questions so it is wise to answer any questions politely and as with vague information rather than specifics. You should not disclose any information about any alcohol you may have consumed. Do not tell police that you only had a couple beers during the game, or that you were at a party or a bar. That information will only lead them to pursue probable cause to further test for DUI or to arrest.
You also have the right to refuse a field sobriety test or chemical test. The field sobriety tests are subjective and can easily be used against you even if you think you can pass them. Your refusal might also frustrate the police officers. If the police threaten you based on your refusal to submit to the tests, you should respectfully tell them that you will perform the test because of their threats but that you do not consent to the tests. That evidence can be used later in court to suppress the results of the tests.
Chemical tests are also subjective because there are medications and conditions which can lead to false positive results on chemical tests. Be aware though that the fact that you refuse the tests can be used against you if your case goes to court and the police officer must make you aware of that consequence. Generally speaking, there are penalties if you refuse a chemical test and some states will use your refusal as a basis to declare for stiff penalties. You always have the right to contact an attorney before you submit to any test.
In most states, police need probable cause before they can make an arrest for driving under the influence. As discussed earlier, probable cause can be made through observations made by law enforcement. The observations are subjective and dependent solely on the police officer's judgment. Police can use observations of slurred speech, weaving while driving, and other impaired actions in order to prove reasonable cause for an arrest. Field sobriety tests can also be used to show probable cause.
There are some states which now allow road check points to check every driver for possible impairment, regardless of how a person appears to be driving. These road check points have been held as constitutional by the United States Supreme Court. It was a divided court where some justices said the importance of stopping drunk driving outweighed the possible infringement of rights to privacy, while some justices felt the infringement was not justified.
Police Officers are allowed to confiscate anything in plain view when they approach your car during a traffic stop. It is always wise to keep things out of plain view. In order for a police officer to search your car, or to look in the glove compartment, or trunk, he must have probable cause or a reasonable suspicion that he will find something illegal. If he does not have a reasonable suspicion, then he will have to get a search warrant to search your car (which also requires a reasonable suspicion). If you were pulled over for a broken headlight, for example, it would be difficult for an officer to justify the need to search your vehicle. However, most drivers allow police to search their cars, and if you consent to a police search, it is legal for him to do so. You should never consent to the police searching your vehicle. If you do not want to be argumentative with the police officer, you can just say nothing, which is the same as not consenting, or you could say that you would like to talk to a lawyer before answering questions or before allowing a search.
Police do not need to read you your Miranda rights until they have you in custody. The police can ask you questions and if you answer the questions, then your answers can be used as evidence in a court. When police are questioning you on the side of the road, you do have the right to be silent, but they do not have to inform you of that right. It is possible to have a conversation with police while remaining polite and respectful without disclosing information which refers to any alcohol you may have had or any other incriminating information. Only after you are under arrest and in police custody do the police have to read you your Miranda rights. At that point, you should ask to speak to a lawyer for DUI and not say anything else.