We demonstrate a proof of concept of a novel and compact integrated mechano-optical sensor for ${\mathrm{H}}_2$ detection based on a microcantilever suspended above a ${\mathrm{Si}}_3{\mathrm{N}}_4$ grated waveguide. The fabricated devices are mechanically and optically modeled and characterized. Sensing operation of the sensor is demonstrated with 1% ${\mathrm{H}}_2$ in ${\mathrm{N}}_2$ . The error in detection of the cantilever bending induced by absorption of ${\mathrm{H}}_2$ is estimated to be approximately $10\mathrm{nm}$ . Significantly improved sensitivity (down to $\sim 33\mathrm{pm}$ ) is expected for reduced initial bending of the microcantilever. The simulation and experimental results are in good agreement and provide a good guideline for further optimization of the sensor.