Field sobriety tests are subjective tests which police officers might ask a driver to perform on the side of the road following a traffic stop. Chemical tests like the breathalyzer can also be used on the side of the road. The most common chemical test is a portable breathalyzer. Some portable breathalyzers cannot be used as evidence but can used to prove probable cause for arrest.
Usually a field sobriety test is taken to prove probable cause. For that reason, it is usually best to politely refuse to submit to the tests. Your chances of passing them are very slim because the police officer makes the determination based on his own judgment. The police can tell you to step out of the car, and you must. When the police ask you to perform tasks in an effort to test your sobriety though (like touching your finger to your nose, or standing on one leg) you can politely refuse to perform those actions.
Most states do require a driver to submit to a chemical test if the police officer has reasonable suspicion that you are in fact impaired. If you were not driving erratically, and you did not admit to having anything to drink, there might not be a reasonable suspicion. If, however, you did admit in conversation with the police that you had some drinks, or if you stumbled during one of the field sobriety tests, or were driving 10 mph under the speed limit, there is enough evidence for the police to have a reasonable suspicion. It is actually an intentionally low bar for police to meet in order to take the next step and do a chemical test. The most common consequence for not taking a chemical test is that your impairment will be implied by your refusal to take the test. Sometimes there are automatic severe penalties for anyone who refuses the chemical tests.
State laws vary as to the time in which tests must be administered, but most state the tests must be administered anywhere from two to four hours after driving. Some tests are administered immediately either roadside, or nearby in a mobile unit (a van with testing equipment). Some tests will be administered later particularly if the driver requests that blood be drawn at a hospital rather than at a police station or a mobile unit.
Implied consent laws are common in most states today. When you get a driver's license in any given state, you essentially agree to submit to any chemical test for DUI if necessary while you are driving under that license. Your driver's license offers the privilege of driving with the implied consent that you will follow traffic laws including submitting to a chemical test. Most states now have implemented an automatic license suspension for driver who fail or refuse to take a chemical test based on this implied consent law.
A preliminary breath test is not admissible in court as evidence of impairment, but it is allowed in most states to establish a probable cause for police officers to take the next step which is a test of blood, urine, or breath for blood alcohol concentration. The more formal tests which can be taken once a probable cause or reasonable suspicion has been established are usually more sophisticated than the preliminary tests are admissible as evidence of impairment in court.
Blood Alcohol Concentrations (BAC) can be tested by taking a sample of blood, breath, or urine. Breath is the least invasive method and the easiest to perform in a mobile unit or roadside, so it is more commonly used. "Breathalyzer" is the common term for the device used to test breath. Another name is the "Intoxilyzer." All breath testing devices have problems and none are known to be always accurate.
Testing blood alcohol concentration by a blood test may be the most reliable test, and if police want you to provide blood for testing, most states allow you to request that you be taken to a hospital for giving the sample, rather than giving a sample at a police station or a mobile unit.
A urine sample can be taken to test for alcohol, but it is not an appropriate indicator for blood alcohol concentration at the time of an arrest. It takes longer for alcohol to enter the digestive system (and appear in urine samples) so alcohol found in urine samples is an indicator that there was alcohol in the system hours or even days before the sample was taken, but not necessarily at the time a driver was behind the wheel of a vehicle.
Usually you will not have a choice of what kind of chemical DUI test is done. Different police districts use different methods depending on their equipment and training and may have different DUI penalties by state. If you do have a choice, remember that the least invasive method would be a breath test, and that is also likely the easiest to argue if you are charged with DUI and have to appear in court.
Blood alcohol concentration can vary depending on whether the individual is a man or a woman. A man and woman who have the same number of drinks will not have the same blood alcohol concentration. It takes fewer drinks for a woman, or a person who weighs less, to register a higher blood alcohol concentration. If you have been drinking on an empty stomach, you might also register a higher blood alcohol concentration than someone who was eating. Drinking slowly over the course of an evening will produce a lower blood alcohol concentration than binge drinking.
The lesson here is that different people can drink the same amount of alcohol but have very different blood alcohol concentrations. It is also important to remember that all drinks are not created equal. A tall 20 oz. glass of beer has much more alcohol than a 12 oz. bottle of beer. A Long Island Iced Tea can have as many as 7 shots and would then be equal to 7 drinks in one glass!
Alcohol affects the central nervous system and when ingested, it passes from the stomach to the small intestine. The alcohol is quickly absorbed into the blood and distributed through the body. The quick absorption results in faster effects on a person's nervous system even with small amounts of alcohol. While most states use .08 as the level at which a DUI charge can be brought, the American Medical Association defines the level of impairment as a BAC of 0.04. A BAC of .35 can result in a coma or death.
Test results can always be challenged. There are so many factors which can play into a reading of BAC. There are flaws in all the testing methods and those flaws may be a factor in your defense. A test result which shows your blood alcohol concentration to be high does not mean you have no defense.
The standard field sobriety tests are physical feats which you would be asked to perform on the side of the road, or off the shoulder. One test requires the driver to walk along a line. Another requires the driver to stand on one foot with the other foot raised 6 inches off the ground. The police officer looks for signs of wobbling, inability to stand, inability to walk and remain steady. The officer will also observe your reactions to the test and will likely engage you in conversation during the tests because you may be distracted by the actions and share information you did not share while being questioned in the car. Another test involved stating the alphabet backwards.
Of course some people could not perform any of these tasks even if they were sober, but these tests are simply used to establish probable cause so the police officers can move to the next step of administering a chemical test.
Field sobriety tests are highly subjective and the likelihood of passing them is very slim. There is nothing to be gained by performing the test. There is no penalty for refusing a field sobriety test and the police will need some other evidence to give them probable cause to move to the next step of a chemical test. Be careful that you do not become confrontational about the field sobriety tests though and remember to be respectful when you say that you do not want to perform the tests. If you really have not had any alcohol prior to the arrest, it might be wise to ask the police officer if he has a video recorder in his car and if so, ask that it be turned on to film the field sobriety tests. That will serve as your proof later that you performed all the tasks correctly and that you are so confident in your ability to pass them that you want to be recorded.