Caldwell E-MAX Link is an advanced Bluetooth communication device that enables communication between multiple users up to 12 miles (line of sight). The E-MAX Link pairs to your current hearing protection wirelessly via Bluetooth with compatible muffs, plugs, or with a 3.5mm audio cord for non-Bluetooth hearing protection. Included is a rechargeable battery (optional 3xAA use), with a USB-C charging cord. In the field or on the range, communicating with others has never been easier! Use the Link with any Caldwell hearing protection, including E-MAX Power Cords, E-MAX Pro, E-MAX Pro BT, E-MAX Shadows and E-MAX Shadows Pro. Mfg: Caldwell Shooting Supplies