The Google Nest video doorbell lets you know who's knocking thanks to its integrated camera. It replaces your existing wired doorbell and delivers HD video and bright, crisp images, even at night. It is designed to view people from head to toe. It sends motion and sound alerts and can recognize your family members or friends and send a special alert. With its 24/7 streaming, you can check in at any time or go back and look at a 3-hour snapshot history to see what happened.