Wearable devices can be used for monitoring vital human physiological signs and for interacting with computers. Due to the limited lifetime of batteries, these devices require novel energy harvesting solutions to ensure uninterrupted and autonomous operation. We therefore developed a wearable wristband device with piezoelectric transducers, which were used for hybrid functionality. These transducers were used for both energy harvesting and sensing applications. In fact, we also demonstrate that gestures can be classified using electricity generated from these piezoelectric transducers as a result of tendon movements around the wrist. In this paper, we demonstrate how a multi-physics simulation model was used to maximize the amount of harvestable energy from these piezoelectric transducers.