Battery Doorbell Step Up, Sleek Design Blends With Any Decor, 3 Sound Options For Front & Back Doors Set At Button, Uses Two 3V Lithium Batteries, Included, 2-1/4" Speaker For Realistic Sound, Adjustable Volume Control, Uses 4 "C" Cell Alkaline Batteries, Not Included, 32 Selectable Codes To Block Outside Interference, Up To 150' Operating Range, Expands With Add-On Doorbells/Chimes RC3523, Rc3253 &/Or Additional Buttons RC3301, RC3302, RC3311, RC3321, 5 Year Warranty.