A breath analysing and training assembly adapted to detect the carbon dioxide(CO2) concentration in the breathing gas of a user, the assembly comprises a selective colorimetric CO2 detector provided with a detector surface adapted to change color rapidly and reversibly with the concentration of CO2,when exposed to CO2, and an adapter comprising -a docking part for receiving a mobile unit comprising an image capturing means, a display, and a processing means,wherein the docking part is configured to position said image capturing means in a fixed relation to said colorimetric detector, such that said image capturing means is adapted to capture images of said detector surface, -a detector holding part adapted to receive said colorimetric detector,wherein said adaptor includes a detector surface protecting means adapted to protect the surface from ambient air in an airtight fashion when no measurement is performed, -a breathing conduit to lead breathing gas to and from said user such that at least a part of the breathing gas passes the detector surface, wherein said processing means is adapted to execute an application program adapted to perform a measurement session including a measurement step for measuring CO2 concentration changes in breathing gas by identifying color changes of images of said detector surface captured by said image capturing means.L'invention concerne un ensemble d'analyse et d'entraînement de respiration conçu pour détecter la concentration de dioxyde de carbone (CO2) dans le gaz respiratoire d'un utilisateur, l'ensemble comprend un détecteur de CO2 colorimétrique sélectif ayant une surface de détecteur conçue pour changer rapidement et de façon réversible de couleur en fonction de la concentration de CO2, lorsqu'elle est exposée au CO2, et un adaptateur comprenant - une partie d'entrée pour recevoir une unité mobile comprenant un moyen de capture d'image, un dispositif d'affichage et un moyen de traitement, la partie d'entrée étant configurée pou
