Physen Wireless Doorbell Kit Bionic Push Button For Door Chime, Accessory:Transmitter (Accessory:Transmitter CW) Accessory: transmitter, perfectly match with Model B (Music Symbol) / Model C (Circle Symbol) receiver Each push button can be freely matched with receiver(door chime) A perfect use case scenario for this product would be if you have a front door and a back door , you can program each push button to a different tone so you can know which door someone is at Powered by 23A 12V Alkaline battery(Battery Included), you need to open the push button to get battery in Choose the quantity of transmitter (push button) as you need , it will bring you an easier & happier life !