The feasibility of detecting the chlorofluoromethane (CFM) onto the outer surface of pristine silicon carbide nanotube (SiCNT), as well as its germanium doped structures (SiCGeNT), was carefully evaluated. Density functional theory level of study using the PBE0 functional together with a 6-311G(d) basis set has been used. Subsequently, the B3LYP, CAM-B3LYP, ωB97XD, and M06-2X functionals with a 6-311G(d) basis set were also employed to consider the single point energies. Natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM) were implemented by using the PBE0/6-311G(d) method. The total density of states (TDOSs), Wiberg bond index (WBI), natural charge, natural electron configuration, donor–acceptor natural bond orbital interactions, and the second-order perturbation energies are performed to explore the nature of the intermolecular interactions. All results denote that by adsorbing of the gas molecule onto the surface of the considered nanostructures, the intermolecular interactions are of the type of strong physical adsorption. It was revealed that the sensitivity of the adsorption will be increased when the gas molecule interacts with decorated nanotubes and decrease the HOMO-LUMO band gap; therefore, the change of electronic properties can be used to design suitable nanosensors to detect CFM gas.