... ,can be uesd in offices,workshops,homes,buildings ect.Using the 2.4G Communications Channel, full-duplex interoperability intercom, communication ... every four seconds3,CALLA:First press the ID number, then the CALL button, enter the main CALL with the red lightB:No response signal 4 ... hear a "beep". Host can hang up on the call of the process. E:The indoor monitor is busy, then drops twice, busy ...