<p>Acetone is a widely used volatile organic compound (VOC) with significant industrial relevance. However, exposure to elevated concentrations (10⁴–10⁵ ppm) poses serious health and safety risks due to its toxicity and flammability. Rapid and reliable detection of such high acetone concentrations remains challenging for many existing sensor technologies. In this work, we demonstrate that low-cost, commercially available, uncoated silicon microcantilevers (Si MCs) can serve as effective gravimetric sensors for high-concentration acetone monitoring with fast response under ambient conditions. The sensor exhibits two distinct sensitivity regimes across the investigated acetone concentration range, and is attributed to variations in surface site availability and progressive saturation effects. The results are further interpreted quantitatively using adsorption isotherm analysis, with the Sips model providing the best fit to the experimental data. A fast response time of 38 (± 8) s and recovery time of 100 (± 5) s were achieved, under ambient conditions. The sensors further demonstrate low hysteresis, good thermal and long term stability. These results establish the potential of uncoated Si MCs as robust and fast-response gravimetric platforms for monitoring high acetone concentrations under ambient conditions.</p>