Replace your old doorbell with the Xsarius Smart Doorbell Pro. Install and pair your doorbell with your smartphone or tablet using the free Xsarius app, available on Google Play and the Apple Store. This allows you to see who is at your door and communicate using the two-way audio function from wherever you are. The doorbell detects activity at your home, and you will automatically receive a notification on your smartphone or tablet. This way, you always know what's happening at your door.