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 2 tones (intermittent and continuous) over 2 channels. It allows for use of both channels, by connecting 2 of the 7 available contacts of the wiring module.RSL-SMM contains 16 tones (mixed types) over 2 channels. It allows for use of both channels, by connecting 2 of the 7 available contacts of the wiring module. For each channel it is possible to select the sound via DIP switch prior to assembling the unit.