Jamie Siminoff spent much of his twenties and thirties as a serial entrepreneur, launching three tech businesses you've probably never heard of. When he finally landed on a breakthrough idea, he didn't realize it at first; he was just trying to solve his own frustration of not being able to hear the doorbell while tinkering in his garage. His jerry-rigged solution evolved into Ring—a doorbell with a camera and microphone that connects to a smart-phone app. After a nail-biting appearance on Shark Tank and a nearly disastrous launch, Jamie was able to rebrand and grow the business, eventually selling to Amazon for roughly $1 billion.