The makers of a widely-used alcohol breathalyzer claim trade secret when asked to reveal programming details of their device; and as a result, some evidence produced by their device, the Intoxilyzer, was tossed out of court in a case upheld by a Florida appeals court back in 2004:
"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 5th District Court of Appeal ruled…
Similar challenges have arisen in Florida and elsewhere, with conflicting court decisions that will eventually require resolution by higher courts, probably eventually by the Supreme Court. This AP report at Fox reviews the whole history of the controversy.
[Link via Rational Review.]