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Are breath testing machines accurate?

Breath-alcohol testing machines like the Breathalyzer, Intoxilyzer, and Alcotest, are used by law enforcement across the nation. Although police agencies are required to use devices approved by the National Highway Traffic Safety Administration, they generally choose one provider or another based on competitive contract bidding.

That's because breath testing machines are made by for-profit companies. Since the underlying source code is proprietary to those companies, it can be hard to tell how they work or how accurate they really are.

Many defense attorneys have come to suspect that some breath testing machines are not always accurate. In cases where the accuracy of these tests has been challenged, the defense has been allowed to examine the source code while protecting the proprietary information from public release. In some cases, challenges have led to DUI charges being dismissed or defendants being acquitted.

The Alcotest 9510 is under scrutiny for potentially inflated results

Although many brands have been challenged, a recent report casts significant doubt on the validity of tests on the Alcotest 9510, manufactured by Draeger. In a 2015 DUI case from Washington State, two software engineering experts were asked to examine the source code of the Alcotest 9510.

They returned a report in which they expressed skepticism that the Alcotest 9510 provides reliable test results under all circumstances. That report has just been released -- and then un-released due to intellectual property concerns. The case has not yet been resolved, but the report has not been seriously challenged.

The two experts found a number of issues with the source code and the configuration chosen by Washington State. For example, they found that a fuel-cell sensor would produce increasingly inflated results as it was depleted. There is a formula in the source code meant to account for that issue, but it only does so for six months before needing recalibration. However, Alcotest machines are supposed to need recalibration only once a year.

This is not the first case in which problems with the Alcotest 9510 have been identified. Last year, a Massachusetts attorney and a computer forensics expert examined the source code and found a number of issues that could cause inflated test results under some circumstances. They noticed the issue with the fuel-cell sensor, as well.

Unfortunately, no court has yet ruled that the Alcotest or any other breath testing machine is itself so unreliable that its results cannot be admissible in court.

Are these tests always accurate? There is reason to suspect they may not be. The good news is that DUI defendants have the right to challenge the accuracy of breath test results, even if that means digging into the source code of the testing machines.

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