An Arizona Judge has approved requests to allow the examination of the software in a new generation of machines that examine blood alcohol levels of motorists.

Pima County Superior Court Judge Deborah Bernini ordered CMI, the manufacturer, to hand over the source code of the Intoxilyzer 8000 to representatives of defence lawyers in a joint lawsuit involving 20 drink drive suspects.

Lawyers for the group argue that access to the software behind the device is necessary in order to establish whether breath tests made using the devices are reliable or not. Only some police forces in the state use breath tests while others use blood tests. Attorneys for the defendants successfully argued that suspects have the right to cross-examine their accusers, in this case electronic devices.

CMI maintains that its source code is a trade secret. Meanwhile prosecutors in the Arizona drink driving cases reckon that there are other ways to determine if the device is reliable, arguing the request is a defence ploy designed to get their clients off the hook. Judge Bernini rejected these arguments and ordered CMI to hand over its secret source code to James Nesci, the lead lawyer for the defendants.

The Arizona ruling increases pressure on CMI but it's by no means sure that the firm will comply. Rejection of the request would place defence lawyers in a strong position to get breath-test results against 170 defendants, both in the cases under consideration by Judge Bernini and other cases going through the system, thrown out of court.

The Intoxilyzer 8000 entered service last year and is well liked by squad car cops because of its light weight and general convenience. The kit can be powered from a car's cigarette lighter output. The previous generation of devices - the Intoxilyzer 5000 - was far bulkier, taking up half the back seat and needing a separate energy supply.

Allegedly inconsistent, odd or inexplicable results involving the Intoxilyzer 8000 have led to legal action in six states (Florida, Louisiana, Massachusetts, Minnesota, Tennessee and New Jersey as well as Arizona). A Florida judge also ordered CMI to hand over the source code running the controversial devices but the firm has refused to comply, earning it $1.2m in fines as a result. ®