The ClearSounds CS-IL40 Portable Telephone Amplifier is light and compact making it easy to carry so you are prepared to talk anytime. And its easy installation will have you hearing clearly and communicating more completely in no time. The CS-IL40 Portable Telephone Amplifier is part of the ClearSounds complete line of assisted hearing products that are innovatively designed and competitively priced to improve your quality of life. Compact size designed for easy transport. Quick and simple installation gets your connection going fast. Volume Control and Boost Button boost incoming volume up to 40 dB. Tone Control allows you to "shape" sound to match your hearing needs. Compatible on 99% of telephones. 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. One-Year Warranty. NOTE: In-Line amplifiers will not work on phones where the dial pad is in the handset, such as a Trimline phone. They also will not work with cordless phones. If you need phone amplification and have one of these phones, it is recommended that you replace the phone with one of the amplified telephones.