Pagers, telephones; sound transmission or reproducing machines; radios including two-way radios; video transmission line machines; antennas; radio condensers; electric transformers; vibrators for pagers, telephones and radios; loudspeakers for pagers, telephones and radios; electrical filter units selectively responsive to currents of different frequencies; monitors for frequency modulation radio stations; earphones and headsets; visual display units; computer interfaces; modems; digital optical transmission units, batteries