In this study, we provide essential information of dangerous states in external environments such as extreme ambient temperature. This platform can determine external signals, such as thermal stress, and simultaneously convert them to a readable form. We fabricated alert patches with colorimetric materials, metal nanoparticles, and matrix polymers. Polydiacetylene (PDA), a family of conjugated polymers, has attracted attention in the field of sensors to read fluorescent, and optoelectrical properties. The highly ordered lamellar PDA architecture showed that the electrical current synchronizes with its color transition (blue-to-red) and the transition was reversible. The conductive nanoparticles provided current reversibility. The potential advantages of this alert patch include simple fabrication and continuous monitoring by thermal stresses. Furthermore, this system can find wide applicability in wearable patches on clothes, skin, and surfaces of materials.