Workers at UCSF Medical Center and Zuckerberg San Francisco General Hospital are wearing the devices, and Oura has asked another 150,000 users to share their data. The rings aren't exactly comprehensive trackers, but they do record body temperature, heart rate and other vitals. In the near term, they could alert medical workers if they have a fever or impending illness, not just COVID-19. By the fall, when some expect the coronavirus to resurge, UCSF and Oura hope to have an algorithm that will detect early symptoms of the virus, so that people can more effectively self-quarantine.

One of the strategies at the epicenter of the coronavirus outbreak in Wuhan, China, was to have residents report their temperatures daily and isolate at the first sign of fever. The ring could allow users to do the same. But it would require that they hand over medical data, which opens up data privacy concerns.

There is some indication that this could work, though. Thanks to the Oura Ring, a Finnish business executive noticed that his temperature was higher than normal (about 100.4 Fahrenheit) and his heart and breathing rates were slightly increased. While he reportedly felt normal otherwise, he had just been traveling in a coronavirus hotspot, so he was tested. The results were positive for COVID-19. Without the ring, he wrote on Facebook, he would not have noticed those changes.