A gas detector device comprises at least a VCSEL source and at least a light sensor for detecting a light beam having passed through a sample chamber containing a given gas to be detected. A second mounting element is provided and is attached at the in-cabin surface of the vehicle windshield at or near or at least partially around the first mounting element. The test set may contain memory to locally store certain technical information, e. The CPT may also be used in other operations involving the polygon, such as in imparting appearance characteristics to the polygon. The driving circuit causes each of the modulated signals to fall in a plurality of level steps.