The W6KM handset builds on the proven W6 by adding the TOUCHSWITCH volume control. Light pressure on the + end of the switch increases the listening volume; light pressure on the - end decreases the volume. An important feature of TOUCH-SWITCH is that the volume automatically resets to normal when the handset is hung up allowing the W6KM to meet ADA requirement; each user can set the volume according to individual need. The W6KM is compatible only with phone systems using carbon microphones. Amplifier Receiver Handset, Provides Increased Volume to the incoming sound under a variety of conditions, Thumb Wheel Volume Control, Distortion Free Amplifier. Pearl.