Described herein are devices for detecting the concentration of acetone gas. Some gas sensor devices comprise: a gas sensor element that includes a boron-doped the polycrystalline n-type semiconductor epsilon WO3. In addition, multi-detector gas sensor elements are also described including at least one based on the aforementioned gas sensor element where the other elements differ in material properties. In addition, methods for detecting acetone gas based on the disclosed elements are also described.