<p>Highly sensitive gas sensors play an important role in applications, such as environmental monitoring, medical diagnostics and food testing. This paper reviews recent advances in metal-doped and noble metal-decorated chemo-resistive gas sensors with different nanostructures (ZnO, SnO₂, In₂O₃ and Fe₂O₃). It mainly includes the doping of metals such as Al, Fe and Cu, and the modification of noble metals such as Pd, Pt and Au, and introduces the bimetallic-modified materials possessing greater advantages than single metals in enhancing gas-sensitive performance. The results and problems of room-temperature detection of perovskite and metal oxide composite structural materials are also discussed. In addition, the potential applications of micro-electro-mechanical system (MEMS) gas sensing arrays and electronic nose smart sensing devices in disease diagnosis and environmental monitoring are presented through their limitations and development trends in areas such as smart homes. Finally, the main challenges and future prospects of metal oxide gas sensors are presented. </p>