Built-in level-dependent function lets wearers hear ambient sound, such as conversation, machine sounds and warning signals. Headset designed for tough environments. Amplifies weak sounds; attenuates sudden impulse noises at harmful levels. It's easy to connect a mobile phone or external communication radio, regardless of the frequency. For safety reasons, the external system has signal priority. Connect an mp3 player or FM radio and listen to news and music. 121 sub-channels allow several users to communicate individually using the same channel. Up to 1 kilometre range.