System Sensor WBB is a weatherproof back box for use with: ? H12/24K, S1224MCK, P1224MCK, and P12015K series SpectrAlert wall horn, strobe and horn/strobe models ? SSM24 and SSV120 series alarm bells NOTE: The weatherproof or outdoor notification appliance must be used with the System Sensor WBB back box when installed in applications requiring the appliance to be weatherproof or outdoor-listed. In such applications, using a back box other than the System Sensor WBB will void the UL designation. NOTE: All System Sensor weatherproof wall-mount horns and horn/strobes can be surface mounted or flush mounted when used with the System Sensor WBB.