This chapter introduces a novel approach that combines structural advantages, nonlinear motion coupling, and displacement-dependent nonlinear damping to achieve tunable resonant frequencies—from high to ultralow—and significantly improved energy harvesting performance. Two bender-type bimorph piezoelectric beam configurations, the vertical-bender and horizontal-bender, are analyzed, with the X-harvester prototype (featuring the vertical-bender) demonstrating a broad, band-pass-like harvesting bandwidth across the ultralow frequency domain. The integration of motion coupling markedly enhances power density and bandwidth across all axes. Under vertical excitation (2 mm), the harvester achieved a continuous DC output of 15 V over an 11 Hz bandwidth (5–16 Hz); under in-plane rotational and horizontal excitations, it produced 6 V (2.6–13.7 Hz at 1.5 mm) and 2 V (3.6–15.6 Hz at 2 mm), respectively—performance metrics that surpass those reported in existing literature. Peak power outputs reached 0.55 mW (6 Hz, 5 mm vertical), 0.113 mW (11 Hz, 1.7 mm rotational), and 0.12 mW (12.25 Hz, 1.5 mm horizontal). Experimental validation confirmed the system’s capability to power IoT-enabled autonomous sensing applications—including a TPMS, HR/ECG sensor, and THMS—using only ultralow frequency vibrations (2.5–6 Hz), enabling real-time monitoring of driver health and safety.