Temperature data collected by wearable devices worn on the finger such as a ring can be reliably used to detect the onset of fevers, a leading symptom of both Covid-19 and the flu, say researchers.

In a study, published in the journal Scientific Reports, more than 65,000 people wearing a ring manufactured by Finnish startup Oura, recorded temperature, heart rate, respiratory rate and levels of activity.

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The goal of the study is to develop an algorithm that can predict the onset of symptoms such as fever, cough and fatigue, which are characteristic of Covid-19.

“With wearable devices that can measure temperature, we can begin to envision a public Covid early alert system,” said study author Benjamin Smarr from the University of California, San Diego in the US.

Wearables such as the Oura ring can collect temperature data continuously throughout the day and night, allowing researchers to measure people’s true temperature baselines and identify fever peaks more accurately.

“Temperature varies not only from person to person but also for the same person at different times of the day,” Smarr said.

The study highlights the importance of collecting data continuously over long periods of time. Incidentally, the lack of continuous data is also why temperature spot checks are not effective for detecting Covid-19.

These spot checks are the equivalent of catching a syllable per minute in a conversation, rather than whole sentences, Smarr said.

In the study, the research team noticed that fever onset often happened before subjects were reporting symptoms, and even to those who never reported other symptoms.

It supports the hypothesis that some fever-like events may go unreported or unnoticed without being truly asymptomatic,” the researchers wrote.

Wearables therefore may contribute to identifying rates of asymptomatic illness as opposed to unreported illness, which is of special importance in the Covid-19 pandemic.

“We need to make sure that our algorithms work for everyone,” Smarr said.

In future, researchers plan to expand their early detection methods to other infectious diseases, such as the flu.