Apparatus for recording, transmission or reproduction of sound and images; mobile and wearable digital electronic devices for recording, organizing, transmitting, manipulating and reviewing text, data, audio, image and video files; audio processing equipment, namely, limiters, equalizers, mixers and compressors; batteries and battery chargers; battery chargers for use with wireless earphones; wireless chargers; electric batteries; earphones and headphones; headsets for telephones; headsets for use with computers; headsets for mobile telephones; wireless headsets for smartphones; audio speakers; loud speakers; amplifiers; microscopes and their parts; digital audio players; devices for hands-free use of mobile phones; hands-free kits for phones; audio-receivers and video-receivers; media players; digital voice signal processors; wireless transmitters and receivers; wearable computer peripherals; wearable activity trackers; portable wrist-mounted digital electronic device for audio recording and audio playback