Smart doorbells are an extension of your smart home. A smart doorbell has a camera and app for on your smart device. Via the app, you receive push messages when someone rings the doorbell. That way, you'll know that you have visitors even when you're not home. Before you purchase a new smart doorbell, think about how you want to connect it. There are doorbells that you connect to your existing wiring and doorbells that work on a battery.