The switch has 2 positions: One for the high frequency sound and the other for the lower frequency sound. It has a light and switch to select between a high and low frequency sound. Easy to easy. Operates with simple connection to phone line.
Telephone Amplifier Practical Extra-Loud Sound Wall Hanging Durable
Cell Phone Headphone Adapter: Retro Type C Receiver, Built-in Microphone, Comfortable Grip, Old Telephone Homewares | Practical Calling Tool for Offices,
Telephone Amplifier Ring Speaker Flasher Bell Easy to Use
Clarity HA40 Telephone Amplifier 40dB Hearing Aid Compatible Untested
