Monitoring and detection of air decomposition components (ADCs) is an effective approach for diagnosing the faults in air switchgear devices. Herein, the adsorption behavior of three ADCs (CO, NO, NO2) on pristine CSiN and Ag/Au-doped CSiN (Ag-CSiN and Au-CSiN) monolayers was investigated using first-principles calculations. The electronic properties of different adsorption systems were systematically analyzed. Moreover, the gas-sensing performance of these systems was evaluated by the analyses of conductivity, work function, and recovery time, which aims to explore the potential sensitive materials for monitoring the ADCs. The results reveal that the pristine CSiN exhibits weak adsorption towards CO and NOx. However, the doping of Ag and Au atoms significantly enhances the adsorption effects of CSiN monolayer, resulting in a transformation from physisorption to chemisorption, with the adsorption energy values ranging from − 0.73 eV to − 1.45 eV. The related adsorption mechanism is further elucidated through the analyses of density of states, band structures, charge density difference, and electron localization function. Furthermore, both Ag-CSiN and Au-CSiN exhibit excellent sensitivity towards CO and NO due to the moderate adsorption strength and significant changes in conductivity and work function. Specifically, Ag-CSiN exhibits a sensing response of 5.59 × 103 towards NO at 348 K, with a recovery time of 1.45 s. While Au-CSiN shows sensing responses of 498 and 6.00 × 105 towards CO and NO at 298 K, respectively, with recovery times of 2.20 s and 7.06 s. Therefore, Au-CSiN can be utilized a promising and recyclable gas sensor for detecting CO and NO at room temperature, and its sensing performance is unaffected by moisture in the air. This study offers a theoretical foundation for the design of novel gas sensors that can effectively diagnose the faults in air switchgear equipment.