CO 2 gas sensing responses are measured using our in-house fabricated CMOS-MEMS ScAlN-based pyroelectric detector with 12% Sc doped concentration. Leveraging on mid-IR absorption behavior of CO 2 gas caused by interaction of CO 2 with light at 4.26 µm wavelength, our ScAlN-based pyroelectric detector successfully detect CO 2 gas response ranging from CO 2 concentrations of 5000 ppm down to 200 ppm. Gas channel lengths are varied from 6 cm to 10 cm and their respective CO 2 responses are measured. Finally, with N2 as the reference gas, we calculate the gas response percentage change of CO 2 gas at different gas channel lengths and concentration.