The RM-2 Relay Module is used as an end-of-line (EOL) power supervision module for 4-wire smoke detectors. The RM-2 is used with the Polarity Reversal Module PRM4W and DSC FSA-410 series smoke detectors. When the PRM-4W reverses polarity on the smoke detector loop to activate all smoke detector sounders, the RM-2 Relay will continue to operate normally (regardless of input power polarity). Refer to the PRM-2W/4W Polarity Reversal Module