The term voice changer refers to a system of altering a person's voice to either make them sound like someone else or to disguise their voice.

Voice changers change the tone or pitch, add distortion to the user's voice, or a combination of all of the above and vary greatly in price and sophistication. A kazoo

Kazoo

The kazoo is a wind instrument which adds a "buzzing" timbral quality to a player's voice when the player vocalizes into it. The kazoo is a type of mirliton, which is a membranophone, a device which modifies the sound of a person's voice by way of a vibrating membrane."Kazoo" was the name given by...

 can be used as a makeshift voice changer, though it can be hard to understand what the person is saying.

Hardware Implementations

The earliest voice changers were electronic devices usually used over the telephone

Telephone

The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...

 for the purpose of disguise. There are low-priced, small lithium battery

Lithium battery

Lithium batteries are disposable batteries that have lithium metal or lithium compounds as an anode. Depending on the design and chemical compounds used, lithium cells can produce voltages from 1.5 V to about 3.7 V, over twice the voltage of an ordinary zinc–carbon battery or alkaline battery...

-powered voice changers that are used between a phone's mouthpiece and the user's mouth. More sophisticated voice changers have different levels of various distortion effects variable by faders

Fade (audio engineering)

In audio engineering, a fade is a gradual increase or decrease in the level of an audio signal. The term can also be used for film cinematography or theater lighting, in much the same way ....

.