A breath analyzing and training assembly for detecting CO2 concentration in the breathing gas of a user, includes a selective colorimetric CO2 detector having a detector surface which rapidly and reversibly changes color with CO2 concentration, when exposed thereto, and an adapter including: a docking part for receiving a mobile unit including an image capturing element, a display, and a processing element, the docking part configured to position the image capturing element in a fixed relation to the colorimetric detector, such that the image capturing element captures images of the detector surface a detector holding part for receiving the colorimetric detector a conduit for leading breathing gas to and from the user such that part thereof passes the detector surface wherein the processing element measures CO2 concentration changes in the breathing gas by identifying color changes of images of the detector surface captured by the image capturing element.
