Device for measuring the concentration of a predetermined gas, in particular CO2, comprising a cavity, a light source emitting light rays within a basic spectral range including visible and infrared, a detector configured to receive a portion of the light rays within a first predefined spectral range corresponding to high absorption of the predetermined gas, a photodiode configured to receive a portion of the light rays within a second predefined spectral range corresponding to low absorption of the predetermined gas, a control unit configured to calculate the concentration of the predetermined gas by comparing the radiant power received by the detector to the radiant power received by the photodiode.