********** 3.5 mm earphone (audio) jack; 3.5 mm listen only earpiece for the ultimate accessory solution; and its pretty necessary when you dont like to other people listen to your partners private communication in noise environment*****Built inmicrophone and remote speaker with clip; you could clip it to your backpack straps at our shoulder to transmit clear sound*****Durable side ptt; you can push to talk easily with the sensitive big ptt button*****Transmit LED; super convenient for operate the mic to transmit sound for communicating with your partner when color changes*****Compatible with H-777 RT21 RT22 RT-5R RT17 RT18 RT19 RT27 Baofeng UV-5R series BF-F8HP BF-888S Arcshell AR-5 Kenwood two way radio and more