Radiant sound modules add an audible alert to a visual stack light application. Depending on the application need, there are two possible solutions:RSL-SM contains two tones (intermittent and continuous) over two channels. It allows for use of both channels by connecting two of the seven available contacts of the wiring module.RSL-SMM contains 16 tones (mixed types) over two channels. It allows for use of both channels by connecting two of the seven available contacts of the wiring module. For each channel, it is possible to select the sound via DIP switch prior to assembling the unit.