Many intercom master stations carry the model # of your system. For most systems, this model # will be on the outside facing of the master station, or inside any doors on the master station. For many M&S (Music and Sound) or Broan systems, there would be a small sticker on the lower right hand corner, up underneath the lip edge, that would have the model # written there. If you cannot locate your model # at any of these locations, sometimes inside the actual master housing, you'll have the housing model # and it may indicate which master station(s) it is compatible with. If you absolutely cannot locate a model #, consider updating your system using the wiring method. If you have any trouble, please feel free to give us a call at 1-800-221-8227.