Herein, a new type of smart glass fabricated by using a thermoswtichable salt hydrate with a microheater is reported. The supersaturated sodium hydrate solution is clear and transparent at the liquid, however, it turns solid and opaque state after mechanical impact. The nanomaterial-based transparent micro heater is suitable for flexible applications and it consumes low electrical energy due to its high electrical conductivity and high-efficiency of electrothermal effect. Considering the solubility of the sodium acetate in water and chemical properties such as water of crystallization, a phase transition from the liquid state to solid occurs in few seconds with rapid crystal growth of sodium acetate trihydrate. Therefore, it quickly blocks an intense sunlight and provides privacy protection. In reverse, the phase transition from the solid-state to the liquid is simply controllable within a few minutes by the microheater. Finally, we demonstrate a practical application of mechano-thermo-chromic (MTC) device by constructing a system, which operates by an external environment condition such as intense UV light.