A system comprising: a plurality of detectors (110,200) in the same vicinity, each detector comprising a gas sensing element, a motion sensor, control circuitry and two-way communications hardware (260,120); and a central station (140,300) in two-way communication with the detectors, wherein the control circuitry of the detectors is configured to: determine an alarm event based on a signal received from one of the gas sensing elements when a predetermined threshold of a hazardous gas in the ambient atmosphere is sensed, transmit an alarm signal to the two-way communications hardware during the alarm event, determine a man-down event based on a signal received from one of the motion sensors when the motion sensor does not detect movement for a predetermined period of time, and transmit a man-down alarm signal to the two-way communications hardware during the man-down event, wherein the two-way, communications hardware is configured to transmit the gas alarm signal and the man-down alarm signal to the central station and respond to the receipt of a status inquiry from the central station, and wherein the central station (140,300) is configured to determine if the man-down alarm signal received from one detector without a gas alarm signal from that same detector is a false alarm by checking whether there is a man-down alarm signal or a gas alarm signal associated with another detector in the same vicinity. a plurality of detectors (110,200) in the same vicinity, each detector comprising a gas sensing element, a motion sensor, control circuitry and two-way communications hardware (260,120); and a central station (140,300) in two-way communication with the detectors, wherein the control circuitry of the detectors is configured to: determine an alarm event based on a signal received from one of the gas sensing elements when a predetermined threshold of a hazardous gas in the ambient atmosphere is sensed, transmit an alarm signal to the two-way communications hardware during the alarm event, determine a man-down event based on a signal received from one of the motion sensors when the motion sensor does not detect movement for a predetermined period of time, and transmit a man-down alarm signal to the two-way communications hardware during the man-down event, determine an alarm event based on a signal received from one of the gas sensing elements when a predetermined threshold of a hazardous gas in the ambient atmosphere is sensed, transmit an alarm signal to the two-way communications hardware during the alarm event, determine a man-down event based on a signal received from one of the motion sensors when the motion sensor does not detect movement for a predetermined period of time, and transmit a man-down alarm signal to the two-way communications hardware during the man-down event, wherein the two-way, communications hardware is configured to transmit the gas alarm signal and the man-down alarm signal to the central station and respond to the receipt of a status inquiry from the central station, and wherein the central station (140,300) is configured to determine if the man-down alarm signal received from one detector without a gas alarm signal from that same detector is a false alarm by checking whether there is a man-down alarm signal or a gas alarm signal associated with another detector in the same vicinity.