With the detector sounder base, you have the option to use it with a sensor (detector) , or as a stand alone fire alarm sounder. The CAS380 features 4 different selectable tones and 3 adjustable volume settings that can be controlled by the panel, so there is no need to access the sounder to alter these settings. When used as a fire alarm sounder only (no detector), the discreet cover plate can be fixed to the sounder and locked into place if required.