Clear Sounds In-Line Amplifier 40Db CS-IL40 UltraClear tone control allows you to shape sound to match your hearing needs Universal dial provides compatibility on 99% of telephones Volume control and boost button boosts incoming volume up to 40 dB Connects to corded phones with dial pad in base (not designed for cordless and trimline phones) Dimensions 3 7/8"W x 2 1/2"H x 1 1/3"D; Requires 9V battery; 1 Year Manufacturers Warranty