By design, Xbox One respects each person’s privacy. Before it will recognize someone, it lets you know what it can see, and gets agreement that person wants to be recognized.

“Sign in when Kinect sees you, before you pick up a controller or remote control–without even turning on a light or putting down your sandwich.”
“When Kinect is turned on, you can play using its video, infrared, and audio sensors, even when there’s not much light in the room. Turn off Kinect in Settings > Kinect. Your sign-in data will never leave this Xbox. Apps and games you play can only access the Kinect data they need, and they need your permissions for that data to leave the console. Change your sign-in settings in Settings > Sign-in, security and passkey.”

Xbox One sign-in screens as launched on November 22, 2013 by Microsoft Corporation. The teams for these screens included Xbox privacy, legal, sign-in engineering, and design teams.