AbstractActuators triggered by water evaporation have found potential applications in a wide range of emerging fields, including smart structures, power generators, artificial muscles, and soft robots. In addition to poor mechanical performance, conventional actuators raise major economic and environmental concerns due to their expensive and complex synthesis processes with hazardous chemicals and high ecological footprint. Herein, a nacre‐inspired moisture‐responsive actuator is fabricated using graphene oxide (GO) and tapioca starch (TS), a water‐soluble, low‐cost, and eco‐friendly natural polymer. The resultant TS/GO nanocomposite film has excellent mechanical properties and exhibits rapid and autonomous locomotion under moisture attack. Moreover, the actuator demonstrates a bending speed of ≈60° s⁻¹ and has the potential to lift a load up to ten times its own weight. Based on these features, a novel moisture detection alarm system with control and operating circuits is assembled using the TS/GO film. Furthermore, the TS/GO actuator shows that it is capable of mimicking biological structures like flowers and can undergo locomotion even for nonwater vapors like isopropyl alcohol, ethanol, and chloroform.