Monday, July 22, 2024

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On Friday, February 3, the final day of hearings regarding the scientific reliability of the Draeger Alcotest 9510 breath test machines, a representative from Draeger testified that a previously unknown error appears to have been caused because the machines were programmed to use an incorrect value during performance checks and calibration.

The 9510 machines use two sensors to measure blood alcohol: An infrared sensor, as required by statute, and an electro-chemical fuel cell.

During calibration, the measurements of the two sensors are supposed to be within 0.008% of each other. After inspecting over 400 machines, however, none were found to be programmed with that 0.008% value. The Draeger representative acknowledged that as a result, in some instances, the machine “would not be flagging interfering substances.”

The defense bar argued that this new revelation is further evidence of the unreliability of the machines and of the many variables that could influence testing results. The Commonwealth maintained that any variance between the two sensors is irrelevant because the only reported value regarding a subject’s blood alcohol is derived from the infrared sensor.

Judge Brennan denied the defense bar’s motion to continue the hearing until the ongoing investigation into the scope and breadth of this issue is complete. The hearing concluded with closing arguments later that day.

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Joseph Waldbaum

Joseph Waldbaum

Joseph Waldbaum has been licensed as an attorney in Massachusetts for the last nineteen years. He has also been a member of the National College of DUI Defense for fifteen years, routinely attending their national seminars. You may learn more about Mr. Waldbaum through his websites at, or You may also reach him by phone at 978.921.4100 or at

One Response

  1. Can you tell if this error was made from the printed results? Or does a specialist have to physically look at the machine?

    I had a dui in July of 2015, I was convicted and sentenced, but I can’t let it go. I am certain I was under the limit. The test used in my case was the aforementioned.

    I’ve since been tracking news on the Alcotest 9510, waiting for proof there is something wrong with this machine!

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