Since the advent of COVID-19, people have been more sensitive to checking for signs of fever. Now, researchers from the University of Washington have developed an app that turns a regular smartphone into an accurate, easy-to-use thermometer.
A fever is generally agreed to be a temperature of 100.4 °F (38 °C) or above and might be a symptom of a viral or bacterial infection. A low-grade fever has a lower cutoff of 99.5 °F (37.5 °C). But to check your temperature, you need a thermometer, which may not be readily available.
Old-fashioned mercury thermometers are practically extinct, and digital versions can be expensive to buy, but the FeverPhone app transforms your smartphone into a thermometer without any additional hardware.
The researchers coopted the thermistors embedded in run-of-the-mill smartphones that are normally used to monitor the integrity of the device’s internal components, particularly the battery. These thermistors are the same as those used in clinical-grade thermometers, which measure the change in temperature when the thermistor comes into contact with the body.
They realized these sensors could track heat transfer between a person and their phone. Using the phone’s touchscreen to sense contact with the skin and the thermistors to measure air temperature and the rise in heat when the phone touched a body, the researchers began experimenting.
They first simulated a warm forehead using a plastic bag filled with heated water, pressing the phone screen against the bag. They used three phone models to collect data: a Google Pixel 6, a Google Pixel 3, and a Huawei P20. The data they collected was used to train a machine-learning model to estimate body temperature by tracking how quickly the phone heats up and using data from the touchscreen to account for how much heat comes from someone touching it. Once they’d collected enough data, the researchers could calibrate the model to account for variations due to phone accessories such as screen protectors and cases.
Within initial testing done, the researchers set about testing their app using human subjects. They recruited 37 participants, 16 of whom had at least a low-grade fever. Prior to testing with the FeverPhone, participants had their temperature measured using an oral thermometer.
Participants pressed the phone’s touchscreen against their forehead for about 90 seconds, which the researchers found was the optimal time for sensing body heat transfer to the phone. The researchers chose the forehead over other body locations – hands, ears, armpits – because it’s less susceptible to drastic temperature changes in response to ambient air temperature and is a sufficiently large area to make contact with the phone screen.
They found that FeverPhone estimated core body temperature with an average error of around 0.41 °F (0.23 °C), well within the clinically acceptable margin of error.
The researchers will continue to fine-tune their app with the aim of making it available for a wide range of smartphones and smartwatches.
“We started with smartphones since they’re ubiquitous and easy to get data from,” said Joseph Breda, lead author of the study. “I am already working on seeing if we can get a similar signal with a smartwatch. What’s nice, because watches are much smaller, is their temperature will change more quickly. So you could imagine having a user put a Fitbit to their forehead and measure in 10 seconds whether they have a fever or not.”
The FeverPhone app is not yet available to download.
The study was published in Proceedings of the ACM on Interactive, Mobile, Wearable and Ubiquitous Technologies.
Source: University of Washington
