The Musical Doorbell main unit, sold separately, replaces your current doorbell and gives you the choice of sounds to announce your visitors. This Musical Doorbell Auxiliary Speaker is an optional accessory that can be wired to the main unit in order to hear the chime in another room. Up to two auxiliary speakers can be wired to the main Musical Doorbell. It is in the same housing as the Musical Doorbell, but with the electronics removed. No batteries are required. iChime Doorbell Main Unit The Musical Doorbell main unit lets you choose from well over 100 built-in songs, sound effects, and even voice phrases. This electronic door chime is designed to replace the normal wired mechanical door bell in your home. It supports a front door button (both lighted and non-lighted) as well as a back door button (optional). It can be set up to play any particular song or sound, or for more variety, it can sequence through any one of twelve groups such as Holiday, Halloween, Patriotic, Spiritual, Old Favorites, Animal Sounds, Children's, Classical, and more. But the real versatility of this doorbell comes with its unique programmable feature. Using the built in piano-like keyboard, you can easily program in your own song! It even comes with an instruction manual containing the notes for many more popular tunes. A song can be programmed note by note or it can simply be played like a piano and the doorbell will record and playback your composition.