Abstract: A system for detecting the existence of a hazardous condition in an area includes a number of battery-powered detecting units whereby each detecting unit is respectively located within a zone within the area and each detecting unit includes a sensing circuit, a battery level monitoring circuit and a transmitting circuit. The sensing circuit senses the existence of a hazardous condition within that respective zone and generates a hazardous condition alert signal in response thereto. The battery level monitoring circuit monitors the level of the battery powering the detecting unit and generates a battery status signal when the battery is at an acceptable level. The transmitting circuit transmits the hazardous condition alert signal and/or the battery status signal. The system also includes a receiving unit which is responsive to the detecting units and includes a receiving circuit, a battery status indicating circuit and a hazard condition alert circuit.