Most states have "implied consent" laws for motorists, requiring DUI suspects to blow into a breath-analysis machine if asked to do so by a police officer.

"The breath test is an integral part of any prosecution," said Earl Varn, an assistant state attorney in Sarasota.

In Florida, state law currently considers a breath test valid if the machine is approved by the Florida Department of Law Enforcement and the person administering the test is qualified. The law also says that a defendant is entitled to "full information concerning the test taken" if such a request is made.

The meaning of that phrase is the key to the DUI challenges in Florida and other states with similar laws.

DUI defense lawyers insist that "full information" means every minute detail about the Intoxilyzer, including the source code used by its computer processor to analyze breath samples, should be subjected to review by expert defense witnesses. Some judges have agreed.

'A mystical machine'

"It seems to us that one should not have privileges and freedom jeopardized by the results of a mystical machine that is immune from discovery," Florida's Fifth District Court of Appeal ruled in Muldowny's case, which resulted in his charges being reduced to reckless driving.

There also have been successful legal challenges involving the source code of other machines, including a 2005 case in Bellevue, Wash., in which a defense lawyer obtained the code of the BAC Datamaster testing machine, sold by National Patent Analytical Systems Inc.

The tactic has led lawmakers to introduce a measure in the Florida Legislature to clarify that such source codes don't have to be produced for DUI defendants.

Last November, a similar challenge in Omaha, Neb., was rejected on grounds that Nebraska did not have the source code. In Rochester, N.Y., a DUI suspect whose lawyer was seeking the source code was convicted of a lesser charge when the technician who maintained the machine was unavailable to testify.

CMI said there was no evidence that its Intoxilyzer is inaccurate, noting that a review of 80,000 tests in a 2002 Arizona case produced no evidence of mistakes.

The company said also said the source code is not a crucial element in proving the Intoxilyzer's accuracy and was a proprietary trade secret that could create havoc if computer hackers obtained it.

"Exposure of the source code could not only be detrimental to CMI from a commercial standpoint, but it could also be detrimental to customers of CMI," the company said. "Disclosure of this information could compromise the integrity of test data that is stored in the instrument."

Prosecutors such as Varn say if the defense challenges prevail, it would mean each DUI breath test could be subjected to exhaustive analysis.

"We would have to hire an expert to come in and testify in every case to explain the function of the instrument and what the test results mean," Varn said.