In-ear monitors are headphones that have been designed for use as monitors by a live performer. They are either of a "universal fit" or "custom fit" design. The universal fit in ear monitors feature rubber or foam tips that can be inserted into virtually anybody's ear. Custom fit in ear monitors are created from an impression of the users ear that has been made by an audiologist. In-ear monitors are almost always used in conjunction with a wireless transmitting system, allowing the performer to freely move about the stage while maintaining their monitor mix.