When someone is arrested for DUI, one thing a defense attorney might look into is whether the breath test was accurate. These tests can be performed incorrectly, and the machines may be uncalibrated or calibrated improperly. Just as important, the machines are manufactured and marketed for profit, with source codes that are proprietary. That means that there could be hidden issues that lead to inaccurate test results.
Recently, the website ZDNet published an investigation into the Alcotest 9510, a commonly used breath testing machine. (The Alcotest 9510 is not the only breath testing machine to be challenged for potential inaccuracy.) The investigation found good reason to suspect the Alcotest 9510, as configured and used by the Washington State Patrol, may be capable of inflating breath-alcohol test results under certain circumstances. The Washington State Patrol's configuration and options are probably relatively common among police agencies.