<p>The development of multifunctional, flexible, and sustainable wearable electronics is critical for the advancement of next-generation smart systems. In this paper, a dual-functional, self-powered device capable of both piezoelectric energy harvesting and high-sensitivity strain sensing is reported. This device was fabricated using sulfated cellulose nanocrystals (SCNCs) derived from waste tissue. These SCNCs were integrated with carbon nanotubes (CNTs) and polyvinyl alcohol (PVA) and supported on biodegradable mulberry paper (MP). It was found that sulfation enhanced the surface charge density, crystallinity, and dipole alignment of the CNCs, thereby significantly improving the piezoelectric performance confirmed with theoretical simulation such as DFT, COMSOL Multiphysics simulation, piezobased dielectric studies and characterization experiments. Based on the experimental demonstration, the optimized composite device exhibited an open-circuit voltage of 6–8&#xa0;V and short-circuit current of 120–150 nA under mechanical deformation. Furthermore, it demonstrated a rapid response (0.5–2&#xa0;s) and high sensitivity of more than 80% in detecting physiological motions, such as the human pulse, finger bending, and neck movements. In addition to energy harvesting, the device exhibited reliable strain-sensing capabilities when mounted on various body parts. Practical demonstrations included integration with Arduino-based circuits for real-time applications, such as smart doorbell systems and safety line-crossing detection, wherein electrical signals are converted into wireless alerts. This combination of sustainability, flexibility, mechanical robustness, and dual functionality highlights the potential of the developed SCNC-based platform for use in self-powered wearable electronics with promising implications for health monitoring, interactive interfaces, and eco-friendly smart devices.</p> Graphical abstract <p></p>