The iChime Doorbell main unit, sold separately, replaces your current doorbell and gives you the choice of sounds to announce your visitors. This iChime 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 iChime unit. It is in the same housing as the iChime itself, but with the electronics removed. No batteries are required.iChime Doorbell Main Unit The iChime Doorbell main unit lets you choose from six built-in categories of songs, sound effects, and even voice phrases. This electronic door chime is designed to replace the normal wired mechanical doorbell 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 setup to play any particular song or sound, or for more variety, it can sequence through any one of six different groups: Classic Chimes, Holiday, Halloween, Old Favorites, Fun Sounds, and Special Occasions. But the real versatility of this doorbell comes with its unique programmable feature. Using the built in microphone or the audio input jack, you can easily record or download up to 6 different songs or sounds