This article presents a novel multiband piezoelectric microelectromechanical systems (MEMS) microphone. Equipped with a fully clamped membrane and a closed-loop frequency-tracking system, the proposed microphone achieves acoustic signal detection in both infrasonic and audible frequency bands (with an experimentally verified bandwidth of 0.1 Hz–3.8 kHz). Key innovations include: 1) concurrent infrasound and audio-band operation via a single structural design; 2) piezoelectric actuation-enabled mechanical modulation of acoustic signals to support frequency and amplitude modulation (FM/AM) readout in the low-frequency regime; 3) an optimized electrode pattern tailored for low frequencies to enhance FM/AM sensitivities; and 4) cost-effective performance realized using standard piezoelectric MEMS processes. Experimentally, for audible detection, the microphone attains a baseline sensitivity of −52 dB (re 1 V/Pa) and a signal-to-noise ratio (SNR) of 61.1 dB. For low-frequency detection, it exhibits an FM sensitivity of 109.3 mHz/Pa and an AM sensitivity of 51.1 V/Pa, achieving 2.7 and 2.2 SNR improvements over the unmodulated signal at 20 Hz. With customized configurations, the FM and AM sensitivities are further enhanced to 1198.9 mHz/Pa and 457.6 V/Pa, respectively. The FM enhancement stems from reallocating the original sensing electrode to drive the membrane on the same device, while the AM improvement relies on the revised electrode pattern. These findings demonstrate the device’s great potential as a solution for wearable devices targeting both voice capture and biometric monitoring via subsonic and low-frequency signatures, including heart rate, respiration, and facial movements.