Respiratory monitoring utilizing pulse oximetry and expired carbon dioxide (CO2) measurement has been an operating room standard since the 1980s. Post-anesthesia and intensive care units adopted pulse oximetry shortly thereafter and only recently have embraced expired CO2 monitoring. However, there remains a need for monitoring the respiratory function of patients in low-intensity hospital environments (i.e., other than operating rooms, post-anesthesia care units, or intensive care units), since they frequently experience respiratory compromise that may progress, require tracheal intubation, and may deteriorate to cardiopulmonary arrest. This is especially true in patients with obesity, obstructive sleep apnea, and opioid administration, which are common risk factors. Monitoring for respiratory compromise in low-intensity environments, however, is challenging. This chapter addresses the use of pulse oximetry, expired CO2, photoplethysmography, bioimpedance, and acoustic monitoring in these settings.