Many DWI cases hinge on breathalyzer results. In some instances, what the breathalyzer says may be the only hard evidence that the state has that an individual was operating a vehicle while intoxicated.
It follows that if you can fight radar gun results in a case about traffic tickets, you can also fight breathalyzer results in a DWI case. If you want to challenge your breathalyzer results you must either bring into question the reliability of the breathalyzer machine itself or that of the officer administering the test, as per FindLaw.
While it is not incredibly common for a breathalyzer machine to be faulty on its own merit, this has happened before. For example, in an Iowa court case an individual was able to blow a “HI” reading on a breathalyzer machine while in court and completely sober. Clearly, in this case there was a problem with the machine itself.
Machines can also be perfectly reliable on their own but lack proper calibration. Normally, a police officer will provide testimony that somebody calibrated the machine. If the police cannot provide this testimony, it is possible the courts will not admit the breathalyzer results.
Just like with radar guns, police must have training on breathalyzer devices to use them. If the officer that administered you a breathalyzer test lacked this training, the courts may not admit the results. Additionally, the police cannot do breathalyzer tests whenever they like, otherwise the breathalyzer could be part of an illegal search. The police must prove that they had probable cause to pull you over at the time of the test.