A Florida court will hear arguments on Friday in a case where the accuracy of a breathalyser is being scrutinised because the manufacturer has refused to release the source code.

Lawyers representing more than 150 defendants who have been charged for driving under the influence of alcohol in two Florida counties will file the request.

They argue that they have a right to see the source code of the alcohol breath analyser that was used to determine their clients' guilt.

"None of the [software] programs that was used here is approved," said Robert Harrison, a lawyer representing some of the defendants. 

"The question is whether the difference [between these programs] is material or not. Without seeing the source code, we do not know."

At the centre of the controversy is the Intoxilyzer 5000, a device made by CMI of Ownsboro, Kentucky.  

A marketing brochure for the device claims that it has been used for more than 25 years, and touts it as the "standard for accuracy, reliability and courtroom evidence".

Information on the internet shows that the Intoxilyzer 5000 is being used worldwide, including in Norway, the US and Canada. CMI did not return repeated phone calls seeking further information.

Florida approved the Intoxilyzer 5000 in 1993, but the manufacturer has since made numerous changes which Harrison argues have not been certified. CMI had to recall its devices in at least one case due to a software error, he said.

Releasing the source code of the device could take away any doubt about its accuracy, but the manufacturer has said in the past that it refuses to do so because it considers that information a trade secret.

This refusal could have far reaching consequences, potentially giving those convicted of 'Driving Under the Influence' a reason to appeal against their rulings.

It also has caused a backlog of such cases that await the results of this case to determine whether evidence gathered by the Intoxilyzer 5000 is still admissible in court.