As has been discussed throughout our help center, the Datamaster DMT breath test machine is capable of diagnosing issues as the happen during a breath test. One thing that frequently happens is when the Datamaster DMT results page prints out "invalid sample." According to the Datamaster DMT manual, the invalid sample warning happens when the machine recognizes a negative-going slope or alcohol concentration during the delivery of the breath sample. What this means in layman terms is that the breath sample passing through the machine is registering an abnormal result. What this generally means is that there could be issues with mouth alcohol. If this statement continues to register, the officer should test the suspect on a different Datamaster DMT machine.