H₂ is a fuel with advantages that include being recyclable, abundant, and environmentally friendly. It has been intensively studied as an attractive renewable energy carrier. However, H₂ detection is a necessary safety concern, because the fuel is explosive at concentrations above 4% in air. In this study, a very sensitive and reliable visual gasochromic H₂ sensor is fabricated by vacuum deposition for detecting H₂ gas leaks by a simple change of colour. A thin amorphous and nanoporous WO₃ film was deposited on a glass substrate by RF sputtering, and palladium nanoparticles prepared by e-beam evaporation were used as a catalyst to decompose H₂ molecules. We have characterized the structural, optical, and chemical properties of the nanohybrid Pd-WO₃ sensor. The sensor exhibited excellent gasochromic performance upon exposure to 1% H₂ in air with a transmittance change of >50% and a colour difference (ΔE) of 52 after 10 min exposure. All fabrication was done at room temperature, and the development of a flexible sensor is described.