Ring a bell, sound a siren, trigger a strobe.  Just connect this signaling relay between your Aiphone intercom, and the device you are activating.  Relays are useful for extending the reach of an intercom system to places in the building where you don't typically go, but need to be from time to time, and need to be alerted if there is a visitor calling in at your door station(s). Intercom supplies power to the input of the RY-ES relay.  A separate power source is required for the external device you are triggering.