A system for redundantly detecting a gas is provided. The system includes first and second series-connected gas sensors and a signaling module. If both gas sensors are functioning normally, the signaling module provides an alert when both gas sensors detect a predetermined gas concentration. If however any one of the gas sensors is experiencing a fault condition, the faulty gas sensor's alarm is shunted by operation of a fault relay, and the signaling module provides an alert when the non-faulty gas sensor detects a predetermined gas concentration. If both gas sensors are experiencing a fault condition, both gas sensors' alarms are shunted by fault relays, and an audible and/or visual alert is generated by the signaling module. Embodiments of the present invention are well suited for industrial facilities, manufacturing facilities, research and development laboratories, and other locations where unsafe gas concentrations may become present.