As a classic flexible material, hydrogels show great potential in wearable electronic devices. The application of strain sensors prepared using them in human health monitoring and humanoid robotics is developing rapidly. However, it is still a challenge to fabricate a high-toughness, large-tensile-deformation, strain-sensitive. and human-skin-fit hydrogel with the integration of excellent mechanical properties and high electrical conductivity. In this study, a flexible sensor using a highly strain-sensitive skin-like hydrogel with acrylamide and sodium alginate was designed using liquid metallic gallium as a “reactive” conductive filler. The sensor had a low elastic modulus (30 kPa) similar to that of skin, a high-toughness (2.25 MJ m–3), self-stiffness, a large tensile deformation (1400%), recoverability, and excellent fatigue resistance. Moreover, the addition of gallium might enhance the electrical conductivity (1.9 S m–1) of the hydrogel while maintaining high transparency, and the flexible sensor device constructed from it showed high sensitivity to strain (gauge factor = 4.08) and pressure (gauge factor = 0.455 kPa–1). As a result, the hydrogel sensor could monitor various human motions, including large-scale joint bending and tiny facial expression, breathing, voice recognition, and handwriting. Furthermore, it might even be used for human–computer communication.

Smart hydrogels have been known for their remarkable applications in various fields of research. Among these smart hydrogels, magnetically responsive hydrogels are more famous because of the ease of their manipulation and a much quicker magnetic response. However, many magnetic hydrogels exhibit fragile and brittle properties. In this study, a smart combination of salting‐out and cyclic freezing–thawing was utilized for the first time to deal with sodium alginate/polyvinyl alcohol based magnetic hydrogel. The optimized magnetic hydrogel has outstanding mechanical properties with 6.66 MPa at the elongation at break of 282%, Young's modulus of 2.51 MPa, and worked with extension at fracture Wext of 9.31 MJ m−3. The magnetic hydrogel could be easily controlled by magnet, such as swim freely in water when controlled by three‐dimensional electromagnetic field. All the results show that these newly fabricated magnetic hydrogel can also carry out many difficult tasks in terms of magnetic response mechanics. This type of tough and magnetically responsive hydrogels can be used for numerous applications such as in swimming robots, flexible gripper, bionic of natural cartilage.