The silver ones are the Enersound R-120 and are multichannel and in most cases include lifetime warranty; at the press of a button the end user can switch among different channels with different frequencies already assigned to each one. The black or dark grey ones are the Enersound R-100, and they feature a single programmable channel, which can be set to different frequencies but not by the end user. The R-100 includes 3-year warranty.