The “vital capacity” is a crucial biomechanical marker for evaluating lung health, and is crucial for diagnosing conditions that include asthma and chronic obstructive pulmonary disease (COPD). However, existing monitoring devices are often limited by their dependence on an external power source, and are susceptible to environmental impact to reduce the accuracy of detection. This study therefore presents a novel magnetoelectric triggered sensor (MTS) for self-powered vital capacity monitoring, where the sensor can directly convert the respiratory airflow into electrical signals and monitor vital capacity. The MTS maintains high signal stability, even when operating in high-humidity environments, to enable precise monitoring of the Forced Vital Capacity (FVC) and Peak Expiratory Flow (PEF), thereby serving as an effective instrument for evaluating vital capacity function. This work not only highlights the significant potential of this new approach to self-powered spirometry sensing but also paves the way for the development of portable and wearable devices for the monitoring of respiratory disease.