News from Florida:
http://tampatrib.com/floridametronews/MGBUBJ5QK9E.html
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DUI Defendants Skip Charge By Asking How Test Works
Published: Jun 5, 2005

SANFORD - Hundreds of cases involving breath-alcohol tests have been thrown out by Seminole County judges in the past five months because the test's manufacturer will not disclose how the machines work.
All four of Seminole County's criminal judges have been using a standard that if a DUI defendant asks for a key piece of information about how the machine works - its software source code, for instance - and the state cannot provide it, the breath test is rejected, the Orlando Sentinel reported Wednesday.

Prosecutors have said they do not know how many drunken drivers have been acquitted as a result. But Gino Feliciani, the misdemeanor division chief in the Seminole County State Attorney's Office, said the conviction rate has dropped to 50 percent or less.

Seminole judges have been following the lead of county Judge Donald Marblestone, who in January ruled that although the information may be a trade secret and controlled by a private contractor, defendants are entitled to it.

"Florida cannot contract away the statutory rights of its citizens," the judge wrote.

Judges in other counties have said the opposite: The state cannot turn over something it does not possess, and the manufacturer should not have to turn over trade secrets.

The Texas Response to this would be __________________________________ . . .

The last paragraph of the article provides the proper answer. But there is always some judge, somewhere, who thinks he/she knows better than everyone else.

An expert can explain the scientific principle to a degree that a judge can make a judgment on the reliability of the instrument without needing to disclose propietary information. This stuff was challenged by deefense attorneys long ago in Texas and rejected, although I'm not aware of an opinion from an appellate coure.