Oulu, Finland-based Ouraring has raised $5.3 million (5 million euro) to support the development of its first product, a smart ring called Oura that uses heart rate, motion, and temperature sensors to track sleep. Investors weren't disclosed but the company said that 75 percent of the investment came from the United States.

“We are passionate about helping Oura users learn how their body responds to their lifestyle and what they can do to improve their sleep, health, and performance,” Petteri Lahtela, CEO and cofounder of Ouraring, said in a statement. "We live in a world where we’re constantly asked to push harder and stretch our boundaries. Oura wants to change that. Your mental and physical readiness to perform varies significantly from day to day. Some days are perfect for challenging your body and mind whereas on other days your focus should be more on recovery. When you balance your daily load with this essential data you can ensure optimal performance, stay healthy and even increase your capacity - like top athletes do."

The Finnish wearable company first debuted its product on Kickstarter in August 2015. They ultimately raised around $650,000, above an original goal of just $100,000.

"We chose the ring form factor because it is comfortable to wear for long periods of time, meaning you can wear Oura all day and all night," the company wrote on its Kickstarter page. "A ring also fits snugly against your skin and is the most convenient place to accurately capture the body signals necessary for measuring and interpreting your sleep, physical activity and performance related indicators."

Although the purpose is to improve sleep, the ring is designed to be worn all the time -- waking and sleeping. The ring automatically knows when the user is sleeping, but tracks all the time. This allows the companion app to offer insights about how changing activity during the day could improve the user's sleep at night.

The wearable has a three-day battery life, then needs to charge for about an hour in a special ring box.

The company did disclose one investor: Jaan Tallinn, a founding engineer of Skype and Kazaa and a co-founder of the Cambridge Centre for the Study of Existential Risk and the Future of Life Institute.

"Oura has a very visible product at an interesting intersection between health, technology and fashion," Tallinn said in a statement. "The company is riding several growth trends that make its success almost inevitable, specifically miniaturization, battery improvements, and Moore's Law. Oura has a highly capable engineering team, led by effective management, they have created a product that is best in class for wearables."