Though designed to get drunk drivers off the road, breath-testing devices can be highly inaccurate, yielding results as much as 40% too high, reports the New York Times.

After reviewing thousands of court records and interviewing over 100 attorneys, scientists, executives and police officers, The Times concluded that breath-testing machines nationwide may be responsible for putting far too many innocent people behind bars.

In many cases, the devices haven’t been properly calibrated.  Maintaining the machines is the purview of police departments that may have sloppy standards or a lack of expertise with the equipment. In addition, notes the Times report, in some cases officials have used stale or home-brewed chemical solutions that tainted results.

In addition, experts have uncovered serious programming mistakes in the machines’ software.

Then there is the fact that burping, toothpaste, mouthwash and breath mints can all throw off the accuracy of test results. Finally, some machines proved to produce very inaccurate results if a person had a high breath temperature –exceeding 93 degrees—which is not that uncommon.

Despite the fact that the devices are unreliable, the tests have become unavoidable for drivers. Every state punishes motorists who refuse to take the test when ordered by a police officer, notes the report.

The legal system's reliance on breath-testing devices has led to dire consequences with too many people wrongfully convicted based on dubious evidence, reports The Times.  

In most states, the threshold for illegal drunkenness is 0.08 grams of alcohol per 100 milliliters of blood. The only way to measure that directly is to draw blood, but the breath testing machines are easier and require less than a minute to run their calculations.