This product is designed, manufactured, labeled, and packaged for sale to industrial and professional customers for workplace use; it is not intended for consumer sale or use Hearing protector helps protect against harmful noise, whilst allowing ambient sounds to be heard Built-in level-dependent function allows the wearer to hear ambient sounds, such as conversations, machine sounds and warning signals 3.5 mm stereo jack to connect to your mobile phone or two-way radio to hear the call right in your ear Auto power off turns headset off after 4 hours of non-use, to save energy and a low-battery warning informs you when to change batteries Voice guided menu system so no need to take your headset off To reduce the corrosion caused by sweat the electronics are located in the outer part of the cup