In the 1970s the invention of rings that change color depending on the temperature of the wearer started a fad. Today a more advanced version could help stop a pandemic, although the team testing them warn larger samples are needed before their effectiveness can be confirmed.

“Mood rings” got their name from the claim that temperature variations, revealed in the changing colors of the rings’ liquid crystals, indicated the wearer’s emotions. After a while people noticed this wasn’t a very reliable measure, since slightly higher temperatures could be an indication of anything from excitement to anger to the room, rather than the wearer, heating up.

Mood ring color changes could also indicate a fever preceding a bout of the flu – a drawback for flirting couples but an opportunity for Professor Benjamin Smarr of the University of California San Diego. Might a constant temperature tracker indicate when someone was coming down with a disease, including Covid-19, before they started feeling sick, Smarr wondered.

Working with Finnish company Oura, Smarr has tested something more sophisticated, and perhaps less aesthetically appealing, than retro jewellery store products. Besides temperature, the ring measures heart rate, breathing and physical activity, helping it distinguish between temperatures from running to catch a bus and those caused by the body fighting an infection.

Moreover, by wearing the rings before they got sick, people established their base-line temperatures.  "Temperature varies not only from person to person but also for the same person at different times of the day," Smarr noted in a statement. Science News By knowing what an individual’s temperature should be under specific conditions, the rings could avoid a lot of false positive readings other checks might report.

Smarr is part of a team studying data from 65,000 people who wore the Oura rings from March and let researchers access the data. They are yet to report on how well the rings worked as infection predictors, but in Scientific Reports discuss ring data from the first 50 people in their sample who tested positive for Covid-19.

Thirty-eight of the 50 participants registered higher temperatures before they showed symptoms that made them suspect they were unwell. Indeed, some who were otherwise asymptomatic throught their infections had slight fevers detectable via the rings. The paper notes this finding; "Supports the hypothesis that some fever-like events may go unreported or unnoticed without being truly asymptomatic,"

"With wearable devices that can measure temperature, we can begin to envision a public COVID early alert system." Smarr said. Science News Better still, the rings will probably detect many other infectious diseases, allowing us to nip future pandemics in the bud, and even assist in controlling seasonal, but still damaging, outbreaks of influenza. One ring to rule them all, one might say, where “them” is plagues.

Exciting as these results are, there was wide variation in how fevers initiated and the changes in heart rate that accompanied Covid-19 onset. Consequently, while it was possible to recognize individuals were getting sick in hindsight with knowledge of a subsequent Covid-19 test, constructing an alogrithm that identifies who needs to get tested based on Oura ring data alone remains an unsolved challenge.

For more information about Covid-19, check out the IFLScience Covid-19 hub where you can follow the current state of the pandemic, the progress of vaccine development, and further insights into the disease.