 Noble metal decorated semi-conducting metal oxide, SMO, gas sensors have shown great potential for real-time environmental monitoring, exhaled breath diagnosis, and food freshness analysis due to their unique electronic and catalytic properties. These sensors can be designed with different nanostructures such as nanoparticles, nanowires, nanorods, nanosheets, nanoflowers, and microspheres which allow for improved response, faster recovery time, lower operating temperatures, and ultra-low detection limits. Additionally, noble metal decorated SMOs containing zinc oxide, tin oxide, tungsten oxide, other SMOs, and heterostructured SMOs have been used to create photo assisted room temperature gas sensors and mechanically flexible smart wearable devices. Furthermore, the mechanisms behind the enhanced sensitivity of these sensors, including the electronic sensitization effect and the chemical sensitization effect, have been explored in depth. Finally, the challenges and future perspectives of this technology are discussed. This article was authored by Li Yuanjiu, Leng Shiou, Li Wenmao, and others. We are article.tv, links in the description below.