 Popular systems are the "Skybell", Ring doorbell, Nest Labs doorbell, the Google "Hello", and many others.These consist of a single unit which is located in place of the traditional push-button and in addition to the physical button, contain an HD camera, PIR sensor and WiFi electronics.The device is connected to the home wi-fi network, and notifications of a button-press or detected movement are pushed to a paired smartphone or other electronic device such as a tablet.