Fig. 2.

The 30 USD Kinsa smart thermometer works with a cell phone app that records the users’ temperature history and transmits the values to the company for public health forecasting of the spread of flu and flu-like illness, including COVID-19. Readings from the more than one million Kinsa thermometers in use have allowed Kinsa to establish baseline levels of fever across the United States. The company’s HealthWeather maps, available to the public on the company’s website, show where fever is above the expected levels, a possible indicator of a coronavirus outbreak. The map for 31 March 2020, for example, revealed an increased level of fevers in the New York City area, where COVID-19 cases were surging. Credit: Wikimedia Commons (CC BY 2.0).