The door bell includes a mini camera and an intercom system with a door bell button to be installed outside at the main entrance. There is also a small screen, usually around 4", to be installed inside the house, anywhere convenient for the customer. When somebody is ringing the door bell, the camera and intercom system is activated and people inside the house can see the person's face and can talk to the person through the intercom system.
This device is normally giving to the customer as a deal closer (with the cost included in the monthly fee or upfront charge).
Multiple screens are available at extra cost for customers to have a screen at the main entrance, one in the kitchen and one in the bedroom.