Gates' prediction: "Constant video feeds of your house will become common, which inform you when somebody visits while you are not home."

What we see now: Google bought Dropcam, the maker of a home-surveillance camera, for $555 million in 2014. But that was just the beginning — Ring makes a smart doorbell camera that can let you see who is at your door. There are even cameras like the PetCube that let you control a laser so you can play with your pets while you're away.