Oura is selling both the Horizon and Heritage versions of its wellness-tracking ring on Amazon and will be offering sizing kits through the retailer. The launch is significant because Amazon is one of the world's largest retailers, coming in second behind Walmart in terms of sales, according to a ranking from the National Retail Federation and research firm Kantar. That broader retail footprint could be critical given that Samsung, which is the second-largest smartphone maker and one of the top five wearables companies, will release its Galaxy Ring later this year.

Oura has made a name for itself in the still nascent market for smart rings. It's become a favorite of celebrities like Kim Kardashian and was used by the NBA in 2020 to track potential signs of sickness in the early days of the COVID-19 pandemic. Oura also helped popularize a "readiness score" that collates multiple bodily metrics to provide more context on whether you should work out or take a rest day, an idea that's become a bigger part of health trackers from Google and Samsung in recent years.

But Samsung will be the first household name in the tech world to meaningfully challenge Oura. Samsung teased its Galaxy Ring in January and showcased it more broadly at Mobile World Congress in Barcelona last month. Like the Oura ring, Samsung's upcoming ring is primarily focused on wellness and fitness tracking. 

Although Samsung hasn't revealed full details about the ring just yet, it's acknowledged the product's primary role as a wellness tracker. During the company's announcement in January, Samsung Research America's Matthew Wiggins described the ring as a "powerful and accessible health and wellness device." And sitting down with CNET in January and February, Hon Pak, vice president and head of the digital health team for the mobile experience business at Samsung Electronics, also discussed the Galaxy Ring's health tracking capabilities and how it will funnel health data into Samsung's Health app. 

Smart rings aren't as well-known as smartwatches, but they're generally seen as a more discreet alternative for people who care about monitoring health but don't want to remain tethered to a smartphone.

"A ring can be less intrusive than a watch, and the finger provides a better physiological location for some health metrics than the wrist," Avi Greengart, president and lead analyst at Techsponential, told CNET's David Lumb. 

Oura's expansion also comes after the smart ring landed in Best Buy stores almost one year ago, boosting its visibility among electronics shoppers.