ATTLEBORO -- A routine drunken-driving arrest in North Attleboro has become one of a few test cases in the state in which defense lawyers are challenging the reliability of breath-alcohol testing machines.

Taunton lawyer Francis O'Boy has filed a challenge in Attleboro District Court on behalf of a city man facing a third-offense drunken-driving charge who registered a .19 percent on the breath-alcohol testing machine.

The legal limit before a person is considered intoxi cated is .08 percent.

North Attleboro police use the Alcotest 7110 MK III-C machine, the same machine used by state police and Boston police.

The machine has been banned in four counties in New Jersey over questions about its reliability. O'Boy argued Wednesday that his client has a right to the `` source code,'' the com puter language used to pro gram the machine in order to test its accuracy and reliabili ty.

`` Without the source code we have no way of doing it except on blind faith,'' O'Boy said, adding that the chal lenge is becoming a `` develop ing area of law.''

`` John Adams wrote the Declaration of Rights in the Massachusetts Constitution, Article 12, in which a defendant shall be able to provide all proof favorable to him,'' O'Boy said.

O'Boy wants the breath-alcohol test against his client thrown out.

The defendant, Douglas S. Martha, 45, of 26 State St., Attleboro, was arrested by North Attleboro Patrolman Craig Chapman around 12:30 a.m. in April 2005, according to court records.

Martha was allegedly driving erratically on Kelley Boulevard and failed field sobriety tests before taking a breath-alcohol test at the police station, according to court records.

Martha has pleaded innocent and is free on $750 cash bail.

Assistant District Attorney Roger Ferris argued that the machine used by North Attleboro police has been certified by the state Bureau of Alcohol Testing as accurate and reliable.

`` There are stringent regulations by which this machine must not only be regulated, but calibrated,'' Ferris said, adding that the police officers who operate the machine also are certified.

He said the machine is tested with each use to make sure it is giving an accurate reading by using a test of known sample of alcohol. If there is the slightest variation in the result, the machine cannot be used, he said. In addition, Ferris argued that the `` source code'' is a trade secret held by the manufacturer much like the recipe for Coca-Cola is a trade secret.

Ferris said the defense has no scientific basis to challenge the reliability.

`` Unless the defense can come up with a scientific basis on which to question the authenticity of the machine it's a specious argument,'' Ferris said.

Drager Safety Inc., the manufacturer, says the Alcotest 7110 MK III-C offers `` undisputedly'' the most advanced breath-alcohol testing technology available today.

It uses two different and independent measuring systems, infrared spectroscopy and electrochemical cell technology, to analyze and display breath alcohol results.

The machine has `` the highest possible level of forensic and legal integrity,'' according to the company's Web site.

Judge Emogene Johnson-Smith scheduled an evidentiary hearing Aug. 15, during which O'Boy said he may have an expert testify.

DAVID LINTON can be reached at 508-236-0338 or at dlinton@thesunchronicle.com.