A flexible composite film based piezoelectric nanogenerator has been explored using lead-free (1−x) KNaNbO3-x BaTiO3 NPs (x = 0.02, 0.04, 0.06 and 0.08) (used as KNN-x BTO) nanoparticles (NPs). The composite films were made of KNN-x BTO NPs impregnated into a Polydimethylsiloxane (PDMS) matrix. BTO was doped into the KNN lattice without affecting the orthorhombic phase of KNN. Structural analysis such as XRD and Raman spectroscopy were used to confirm the phase formation and atomic vibrations of the piezoelectric materials. Further the electrical analysis of the piezoelectric composite nanogenerator (PCNG) has been performed and the device generates a maximum electrical output of 58 V, 450 nA. Then the PCNG was used as an active sensor for sleep monitoring system by placing the PCNG in the hands and legs of human body and monitor the body movements. This type of system helps to diagnose the sleeping disorder in humans and to be a future advancement in mobile health care monitoring. © 2019 Elsevier B.V.