Apollo XP95 Sounder Control Unit is used to control the operation of a zone of conventional sounders and report their status to the control panel. The unit is loop powered and operates at 17 to 28VDC. It requires a local power supply of 9 to 32VDC to power the external load, which may be up to 1A. The sounder control unit with isolator is used to control the operation of a zone of externally powered sounders, visual indicators and VADs and to report their status to Apollo compatible control equipment. It allows the devices to be operated continuously or be pulsed, 1 second ON, 1 second OFF. The device may be operated individually or in groups and whichever address mode has been applied, may be synchronised when in pulsed operation. An opto-coupled input is provided to monitor the state of the external power supply. It is normally supplied with a backbox for surface mounting and is intended for indoor use only. The backbox is moulded from the same white self-extinguishing polycarbonate as Apollo detectors.