The Telephone Voice Changer - I disguises your voice by digitizing it. The degree of change can be adjusted as you are speaking by pressing the buttons located on the front of the unit. Features an on/off switch, is 9-volt battery powered (not included) and weighs 3.9 ounces. Pocket sized for portability. Dimensions:4" x 2" x 3/4". Easy hook up and is compatible with all telephones because you simply hold it over the mouthpiece and speak normally.