In every DUI case involving a breath test, an experienced DUI attorney will attempt to successfully have the results suppressed so that they will not be used against their client in trial. Dismissal of the case entirely will likely be the most desired result, but suppression of the breath test is the next best scenario - the less evidence there is, the harder it is for the prosecutor to establish their case. It is not uncommon for a plea agreement to be reached subsequent to a judge granting a defense motion to suppress a breath test result.
For a breath test result to be suppressed in court, the judge must determine that its results are unreliable. Results are said to be unreliable when there are problems with the breath machine itself, as well as the administration of the test. Improper administration includes everything from not having sufficient probable cause to ask a person to submit, to failure to correctly explain the ramifications of refusal, or human error during the test administration. The particular facts and circumstances of your case will determine what arguments will be used by your attorney in a motion to suppress.
Most states have promulgated special administrative rules and regulations that specify precisely how each test is to be administered, as well as how each breath machine is to be maintained, stored, and repaired. Failure to comply with these rules affects the reliability of the result. The more mistakes that are made and procedures that are not followed, the more likely the test result will be unreliable (and thus inadmissible in court).
If a pre-trial motion to suppress your breath test result is denied, that does not mean your attorney will not be able to attack the breath test results at trial. Your attorney must work hard to attack the reliability of the machine and the validity of the result. A detailed investigation must be made to determine the machine's maintenance history, as well as the qualifications of the breath test operator.
Breath test operators must take a special course on test administration. Upon completion of the course they are given a permit that allows them to operate the machine. Every few years the permit expires and a refresher course must be taken in order to renew the permit. If a breath test was administered by an operator with an expired permit, or by an individual who was not qualified to administer the test, your attorney should make that clear to the judge, prosecutor, and/or jury.
Other challenges to breath test operators include human error, such as failure to comply with any of the required testing procedures, mistakes made during the test administration, or improper maintenance and storage of the machine. Common mistakes include test samples taken too late in time, failure to comply with observation period, and failure to properly advise of implied consent warnings.