Apollo XPA-CB-14023-APO XPander Multisensor Detector with Sounder VID Base (Red Flash) XPander sounders are ceiling mounted and use a bi-directional monitored radio platform to communicate. They feature 4 tone pairs, including the Apollo tone, and a self-test which causes a fault signal to be sent if the sounders fail to operate. The address of a sounder or a combined sounder/visual indicator is set at the commissioning stage by means of a DIL switch. The sounder address is plus one of the address set. The sounders and combined sounder/visual indicators are powered by two packs of batteries, one with three AA and one with three C size alkaline batteries which provide a working life of typically 3-5 years. The five-year life includes weekly tests and a half-hour sounding in a fire condition. The Combined Sounders and Sounder Visual Indicators incorporate audible and visual alarm indicators within one unit.