Respiratory gas monitors are being employed increasingly by healthcare providers to ensure respiratory health during critical care procedures such as sedation, mechanical ventilation and CPR. A malfunctioning gas monitor, which can be difficult to detect using traditional static test methods, can lead to serious injury or death. Current calibration and test methods are inadequate and cannot detect many critical fault conditions including leaks in the sampling system, a weak sample pump or valves, inadequate dynamic response and malfunctioning alarms. This project's focus is to develop a patient breath simulator that will allow for the testing of respiratory gas monitors under dynamic conditions encountered during patient use. The proposed device will be portable and will be capable of simulating O2, N2O, anesthetic agent and CO2 concentrations as well as pressure conditions mimicking human respiratory cycles. The same device will have additional testing modes that allow it to detect other critical faults. The proposed device will work with diverting gas monitors as well as on-airway gas monitors. The device is intended for use on both simple capnometers as well as multi-gas anesthesia monitors. The functionality of the proposed device will be verified through a series of bench tests on multiple gas monitors modified to introduce the various fault conditions. Additional verification will be done through usability studies with actua end users. The project will culminate in the beta testing of a larger sample of devices at a number of locations. Successful completion of this project will result in a final design for a marketable device that provides improved gas monitor testing and verification. The ability to detect gas monitor failures under real world conditions using an automated tester will improve patient safety, reduce risk for healthcare institutions, increase test procedure standardization and decrease testing/calibration costs.