TAC-SKY RAC Tactical Headset Communica Pickup Noise Reduction for Fast Helmet ARC Rail Adapter Tactical High-cut Headset RAC PTTNote: This headset is a civilian version only compatible with the civilian version of PTT, (not compatible with the military version of PTT) 1. The guide rail adapter supports FAST series helmets, ACH helmets, MICH helmets and other helmets with ARC guide rails on the side; 2. Sound pickup and noise reduction (install 2 AAA dry batteries, not included); 3. The functions different from other earphones are: indoor and outdoor modes (dual mode is