The Clarity HA40 Portable Telephone Handset Amplifier featuring Clarity Power technology makes telephone conversations not only LOUDER, but also CLEARER and EASIER to understand. 
 
A compact battery unit (including a 9-volt battery) that gives you convenient, portable sound amplificationVersatile, it attaches easily and is compatible with virtually all residential and office phones with a removable handset cord and a keyboard on the base of the phoneCustomize your listening experience with adjustable tone control, which will help with clarity, adjusting the pitch of the soundsTake on the unique listening challenges created by some callers with the volume boost button for extra amplification