UltraClear Sound-Clarifying Technology allows you to shape sound to match your hearing needs. This in-line telephone amplifier is so light, you'll carry it everywhere you go. It boosts volume up to 30 dB, plus the adjustable tone control lets you customize every conversation to suit your hearing. Simply plug into any corded phone with the dial pad in the base, and you're ready to go. Measures approximately 4 inches x 2.5 x 1 1/3 and operates with an A/C adapter and takes one 9 volt battery (included).