We show that the sensitivity of metal-oxide gas sensors to a given gas peaks at temperatures which correspond to specific oxide phonon energies. It indicates that atomic vibrations contribute to the sensing mechanism and explains the dependence of the sensitivity on the exposed facet. In addition, the signature of the molecular vibrations in sensitivity is reported. Lattice anharmonicity as ingredient in shaping the sensitivity peak is introduced. The existence of a resonant charge transfer when the phonon frequency matches a molecular vibration one is brought to the fore.