Use With Or Without A Telephone: Plug it into your telephone or directly into a telephone jack Combine With Portable Amplifier: Use with portable amplifier to create a complete Clarity Power Travel Pack. Combined with our Model CE100 Clarity Power Portable High-Frequency Amplifier, turns any conventional telephone into a full-featured Clarity Power telephone Adjustable Volume: Volume adjustable up to 25dB Visual Ringer Light: Bright visual ringer light flashes when phone rings Line Powered: Powered entirely by phone line; works even when electricity is off; no batteries or electric cord required