BikeMic or microphone for bicycles is a device that you connect in between your headphones and music player (like smartphone). In order to do that you just plug BikeMic cable to headphone jack of your player and headphones cable into BikeMic output. From now on, music from your player is feed into BikeMic. BikeMic has a built-in stereo microphone which record sound of your surroundings and then mixes them with your music in order you are able to listen to both of them simultaneously.