We present a flexible serpentine-structured graphene–CNT paper strain sensor. The chemical bonding and surface morphology of the thin film were characterized by Raman and FESEM. The electrical performances of the serpentine structure device are shown in the form of V(I) characteristics. The behavior of the device in variable temperature environments was tested using a cryogenic setup and the device showed robust performances. The bending measurements were conducted by applying compression and tension force on the device with the help of a stepper motor-controlled linear actuator and the device showed significant resistance variation in the application of tension force. The sensitivity of the fabricated strain sensor was also investigated in the form of gauge factor and application of different levels of strain (from 0 to 0.35%) by varying the radius of curvature. The strain sensor demonstrated a high sensitivity with a G.F. of 118. High durability of the device was observed during 5000 repeatable measurements. Finally, the device was implemented for human activity measurements and showed detectable resistance changes in the wrist, elbow and finger movements at various angles.