Application of pressure sensors. (a) Simulation of Morse code for “IAM” produced by tapping the hydrogel sensor. (b) Sensing performance of the hydrogel sensor under imitated knocking of early-stage Parkinson’s disease. Inset: amplified current variation. (c) Schematic for writing sensing. (d–f) Writing sensing of different English letters (“I,” “A,” and “M”). (g) Photographs of the device for position detection. The relative current change distribution of (h) finger press stresses, (i) a beaker, and (j) a centrifuge tube filled with water.