The adsorption and sensing capabilities of CO and NO on pristine and metal-decorated (8,0) SWCNT were analyzed by DFT. Both gases cause a slight deformation of the nanotube curvature in the direction of molecular adsorption. The molecule's adsorption and sensing performance are enhanced with the transition metal (Sc, Cr, Fe, and Ni) decoration on SWCNT. Decorated nanotubes are suitable for high-temperature sensors. According to relative energies for NO, the operational range is 900–1200 K. For CO/Cr- and Sc-SWCNT between 100 and 200 K and close to 550 K in the cases of decoration with Fe and Ni. From the recovery time analysis, the metal-decorated materials exhibit better performance at high temperatures and low pressures for NO compared to CO. Changes in magnetic moment suggest that Cr-decorated SWCNT could serve as a magnetic sensor for both molecules. Display omitted •The pristine CNT is more reactive to NO than CO.•The transition metal (TM) doping enhances the adsorption energy and sensing performance for NO and CO.•TM-doped SWCNTs are better for sensing NO at high temperature and low pressure.•Recovery time shows that the best sensors for NO are Cr and Ni decorated CNT.•At room temperature, TM-SWCNTs could be effective for absorbing material to clean both gases.