The entrepreneurs at Shark Tank have invested in a number of major products since the show premiered in the U.S. in 2009, but for every hit they've spotted, there have been plenty of missed opportunities. The biggest one that got away was a smart doorbell called Doorbot. After the idea was passed up by five sharks in a row, its valuation climbed higher than any product to appear on the show. Now, Quartz reports that Amazon has bought the business, now called Ring, for over $1 billion.

Entrepreneur Jamie Siminoff pitched his concept to the sharks in November 2013. He framed the product as a "caller I.D. for your front door," explaining that every time someone rang the doorbell, the homeowner would receive a video feed on their smartphone showing the person standing outside.

Siminoff asked for a $700,000 investment for a 10 percent stake, an offer each shark ultimately declined. "This company instead of being worth $7 million, can be worth $80 million, $90 million. I just don't see the progression," Mark Cuban said in the video below.

But Siminoff didn't let the rejection slow him down. He kept building the company, and within four years it was valued at $1 billion and had attracted big-name investors like Virgin's Richard Branson. Now, Amazon has seen the product's potential, not just as a caller I.D. for the home as Siminoff originally put it, but as a home security tool. Ring alerts users every time someone walk up to their door, whether they ring the bell or not, and users can speak to the intruder through their phones to scare them away.

The smart doorbell is now available to purchase on Amazon.

[h/t Quartz]