Oura Ring 4

The Oura Ring 4. The $350 Oura Ring 4 looks sleek and cool, and it may be useful for data-hungry health enthusiasts. (Andria Lo/The New York Times)

The Oura Ring 4. The $350 Oura Ring 4 looks sleek and cool, and it may be useful for data-hungry health enthusiasts. (Andria Lo/The New York Times)

The Oura Ring 4. The $350 Oura Ring 4 looks sleek and cool, and it may be useful for data-hungry health enthusiasts. (Andria Lo/The New York Times)