... intercom called received signal, RED light bright and create sound, will stop sound after two “Ding Dong”, and enter into standby ... status: 1). If the extension intercom is sounding “Ding Dong” then will not repeat “Ding Dong” again, and the calling intercom ... 4s, both red and green light on and sounds Di..,then release all the button, after the green and red light off ...