The Nest Hello $199 succeeds by continuously recording video, so you never have the frustrating experience of firing up the app just to see video of someone walking away. Facial recognition lets you know who's at the door by name, and it can also distinguish between people and cars. What's more, you can separate the field of vision into multiple zones, which helps you customize the notifications. Design and InstallationThe Nest Hello video doorbell is sleek and slim, at 4. 6 x 1. 7 x 1 inches, and has rounded corners. On its face is a round doorbell button lit by a blue ring, with the camera above it. Image credit: NestIts small size leaves no room for onboard power, which means the Nest Hello requires a wired connection with 16 to 24 volts of power. That power requirement can be an issue for older houses — I previously had to get the transformer on my 1946 built bungalow upgraded to get a Ring Pro doorbell with the same power requirements to work. The Ring Video Doorbell 2 and the August Doorbell Cam Pro run on batteries, which makes them easier to install. In addition, Nest requires you to install a small module called the "chime connector" inside your doorbell's chime box, located inside the home.