Helmet non-invasive ventilation (NIV) is a form of continuous positive applied pressure that has emerged as a useful therapy for COVID-19 patients who require respiratory support but may not require invasive ventilation. Helmet NIV has seen an increase in use during the COVID-19 pandemic because it is low-cost, readily available, and provides viral filters between the patient and clinician. Helmet NIV may also provide better patient outcomes by delaying or eliminating the need for invasive ventilation. Its widespread adoption has been limited, however, by the lack of a respiratory monitoring system that is needed to address known safety vulnerabilities and to provide clinicians with a respiratory profile of the patient. To address this safety need, we have developed an inexpensive respiratory monitoring system that is based on readily available commercial components and is suitable for rapid local manufacture. The system is designed for use in conjunction with the COVID-19 Helmet developed by Sea-Long Medical Systems, but is modular and can be used with other ventilation systems. The monitoring system comprises one or more flow and pressure sensors and a central remote station that can be used to remotely monitor up to 20 patients simultaneously. The system reports flow, pressure, and clinically relevant metrics including respiratory rate, tidal volume equivalent, peak inspiratory pressure (PIP), positive end-expiratory pressure (PEEP) and the ratio of inspiratory time to expiratory time (I:E). The device will sound alarms based on clinician-set thresholds. In bench tests using a commercial ventilator and artificial lung system, our device performs comparably to a commercial single-patient respiratory monitor. Results are presented from human-subject tests on a healthy volunteer undergoing helmet non-invasive ventilation. Detailed design and manufacturing documents are provided.