With roughly a 100 foot range, the Set 820 system is enhanced with radio frequency (RF) technology for a larger coverage area, so users can leave a room and won't need to worry about missing a word of the program or song. The stereo stethophone receiver has a large, easy-to-use volume control dial. Two year warranty. Adjustable ear bows with automatic on/off function..... RF wireless transmission..... Stereo or mono operation..... Quick charge feature..... High SPL (125dB)..... Maximum volume and bass response adjustable by hearing professional