Mobile Technology

App will turn a smartphone into an accurate thermometer

Joseph Breda is part of a team that has developed an app that turns a run-of-the-mill smartphone into a thermometer
Dennis Wise/University of Washington
Joseph Breda is part of a team that has developed an app that turns a run-of-the-mill smartphone into a thermometer
Dennis Wise/University of Washington

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

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7 comments
Kpar
This is an extremely clever idea. Waiting for the app.
A.L.
“ Old-fashioned mercury thermometers are practically extinct, and digital versions can be expensive to buy…”

Digital thermometers are ridiculously cheap, $6-$8.
akarp
The main issue with detecting a 'fever' is not the thermometer...its the baseline average temperature of the individual. My Oura ring notified me of a possible infection with a 0.5F increase in temperature. This was when I was doing a placebo controlled vaccine study...so I knew it indicated my body was reacting to the vaccine. But this would have never registered because my body can be a little lower than the '98.6 population average'. Not to mention average body temperature is decreasing over generations.


Also where on/in the body the measurement is taken also affects this.

"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" .... this is only for oral temperature, lol.
Daveb
Sometimes my phone feels warm, so I believe it cycles through various temperature ranges as a result of operating various heat-producing subsystems such as screen, gps, etc. It is probably always in a state of changing temperature due to that, and changing ambient temperature. Even given 90 seconds to add body heat to the phone’s thermal mass, which by the way is 90 times longer than it takes my IR thermometer, I’m skeptical that a body temperature reading done this way could be very accurate. However it does seem that they have obtained some good results, and I’ll bet it was fun working this out. Kudos
Captain Obvious
You can get basal body temperature thermometers under $15 with a repeatability within 0.1 F, which is good enough to detect ovulation, and confirm pregnancy. Half a degree won't cut it. But cool idea though.
itsKeef
not sure how they can avoid the (random) background temperature cycling that occurs in a phone? I would prefer a remote tethered or wireless probe. Its generally accepted that there are six methods of measuring body temperature, Skin, Oral, Tympanic, Axillary, Vaginal and still the gold standard Rectal considered the most reliable and accurate . I guess if the phone is fitted with an infrared emitter one could perform a sort of temporal artery check. Not very accurate tho'
RAG
While if you don't have another choice immediately available, I might use an app, but when I get get my temp almost instantly with today's scanning or infrared devices, not sure I want to wait 90 seconds.