Cobalt Relay Extension Board Cobalt REX is an infinitely flexible set of add-on changeover relays that can be operated all at once or in pairs. Cobalt REX can be used with N.O. or N.C. type switches triggered by detectors and other things. Cobalt REX is very easy to use and totally configurable to meet almost any need. Combine REX and Cobalt-S switches or Cobalt motors and there are NO limits to the control abilities interlocking or any sort of direct device automation! If you want to make REX DCC-addressable simply add an AD1HP to switch multiple devices with a single digital command!