The Serene® UA-45 inline phone amplifier can be attached to any standard corded phone to provide additional handset amplification up to 45dB. Volume control uses a rotary dial for longer life and adjustable tone control has three discrete settings for better precision. This model does not have the additional jack for headset use. Uses one 9V battery (not included).
Product Manual Click Here For Universal Amplifier for Corded Telephone Handsets Instructions