SARASOTA COUNTY -- Defense attorneys are attacking the credibility of one of the county's most powerful tools against suspected drunk drivers: the Intoxilyzer 5000.

The briefcase-sized machine uses a breath sample to let police know if someone's blood-alcohol content is over the legal limit of .08.

But nearly 150 defendants in DUI cases say they need to know how the machine's software works to determine whether the results against them are reliable.

Their attorneys already know the problem: Prosecutors can't give them the software's source code because they don't know it. And the manufacturer of the Intoxilyzer 5000 says the code is a trade secret and won't divulge it.

The same legal tactic has been tried with mixed results in other Florida counties.

Prosecutors say the machines are approved by the state and calibrated monthly, and the source code isn't relevant to the test results.

The software request is the most recent in a series of broad challenges that local defense attorneys have made to the reliability of breath tests, hoping to get test results thrown out of court.

So far, none of the challenges have worked. Breath tests continue to be one of the most damning pieces of evidence in DUI cases.

Three judges who hear DUI cases in Sarasota County and one judge from Manatee County listened to arguments and testimony about the Intoxilyzer 5000 from an expert witness Friday.

Their decision could mean the exclusion of breath tests in hundreds of DUI cases, leaving prosecutors with weaker cases and no choice but to reduce charges in some.

That has happened in Seminole and Orange counties, where judges decided in November to exclude Intoxilyzer 5000 breath-test results from hundreds of cases.

But judges in two other Florida counties have said defendants don't need to know the source code, and prosecutors shouldn't be punished for not turning it over.

"It is the defendant's burden to show that the source code is material to a theory of defense in their case," said Jason Miller, the assistant state attorney fighting the motion in Sarasota County.

The defense attorneys counter by saying their expert witness needs the source code to know whether changes to the machine have altered the software and jeopardized the results.

A decision by the three Sarasota judges at the hearing will likely be made within two weeks and set the policy for the county.

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