Display omitted •Dual-physically cross-linked double network endows hydrogel recoverability and fatigue resistance.•Ca2+ ions provide hydrogel excellent strain-sensitive conductivity.•The hydrogel can be assembled as wearable strain sensor to monitor human-motions.•The monitor of slight physiological activities like talking and breathing were achieved. Soft, stretchable, and elastic hydrogels have recently attracted immense interest due to their potential applications in wearable strain sensors. However, most of hydrogel-based sensors exhibit poor mechanical properties. Here, a robust, flexible and strain-sensitive conductive wearable sensor is prepared based on dual physically cross-linked double network hydrogels consisting of core-shell hybrid nanoparticles cross-linked polyacrylamide as first network and Ca2+ cross-linked alginate as second network. Dynamic physical cross-linking as sacrifice bonds can effectively dissipate energy and reconstruct the network structure, endowing hydrogels with high strength, toughness, stretchability and excellent self-recovery properties. Moreover, the hydrogels exhibit outstanding strain sensitive behavior with repeatable, stable, and precise changes in resistance signals. Based on the excellent strain sensitivity, the hydrogel can be assembled as a wearable strain sensor to monitor joint motions such as finger, wrist, elbow, neck, and knee joints, and even the slight motions including breathing and speaking. Thus, the tough, anti-fatigue, self-recovery and conductive hydrogels have promising potential as soft, high-performance and flexible wearable strain sensor for soft robots, biomimetic prostheses, human activity monitoring and health-monitoring systems.