One of the most frequently asked questions regarding DWI stops is whether or not a driver should submit to a voluntary breathalyzer or blood test when pulled over by the police.Before you can be convicted of driving while intoxicated in the State of Texas, the prosecution must prove beyond any reasonable doubt that you were operating a motor vehicle in a public place while the alcohol level in your blood was over the legal limit, or that you didn’t "possess normal use of your mental and/or physical faculties".
The police are legally limited in their ability to administer certain types of field sobriety tests, and they must rely on your cooperation when performing these tests. Field tests are not always reliable and usually cannot be forced upon a person; in fact all machines used at the roadside are inaccurate for precisely measuring alcohol concentration.
Even if you have not been drinking, several factors can produce a false positive in a field breathalyzer including recent dental work, chemical exposure, and even the Atkins Diet. People who work in the oil field or car body shops and even manicurists are exposed to substances in their work environments which can be mislabeled as "alcohol" by the machine.
The officer may tell you that the results will not be used in court, but this is not true: if you do consent to the roadside test and it reports 0.080 or higher, prosecution of your criminal DWI case has become much easier.
Despite your constitutional protections against self-incrimination, if you refuse a roadside sobriety test the officer will almost certainly arrest you. At this point you will be required to take further, more accurate tests at the police station. Things now become more complicated legally, and it is strongly suggested that you immediately exercise your right to an attorney.
Because Texas has an implied consent clause (Section 724.011 of the Texas State Transportation Code) stating that anyone who is arrested for DWI in Texas "is deemed to have consented... to submit to the taking of one or more specimens of the person's breath or blood for analysis to determine the alcohol concentration or the presence in the person's body of a controlled substance", you have automatically agreed to take an alcohol or drug test if a police officer deems it necessary by the simple act of getting arrested. However, you still have the right to refuse the breathalyzer and the blood test. This refusal could lead to a suspension of your driving privileges for 180 days if this is your first DWI.
If you refuse to take the breathalyzer or blood test or you accept and fail, you have 15 days to request a hearing to save your license. If you don’t request this hearing within 15 days, you can’t stop your license from being suspended. Nonetheless, it is much harder for the prosecutor to convict you if you have refused all sobriety tests because they don’t have any evidence to use against you.
Police have also adopted "No Refusal" policies in some jurisdictions; if a driver refuses to give a voluntary sample, the police will seek a warrant from a judge authorizing them to take a blood sample to determine the driver's blood alcohol content (BAC).