We separate myth from method in measuring body temperature with an iPhone. You will see what works today, what is coming, and when external sensors are the only reliable answer.
Phones keep taking over jobs that used to need dedicated instruments, such as heart rate monitors or oximeters. The Galaxy Note 4, for example, can measure your blood oxygen saturation and give you an estimate of SpO2. Body temperature is a different story. The iPhone has no built-in thermometer, and the apps that promise a reading work in very different ways.
An app on its own can only estimate your temperature, and measuring it with the phone alone is still a research project. For an actual reading, the iPhone needs an external thermometer or sensor.
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Reading Body Temperature With an iPhone
If you search Google, the first app you'll find is Body Temperature App For Fever. It needs a paid subscription. I bought one to see what you actually get.
Before the first measurement, the app asks for your heart rate and breathing rate. Then comes a long questionnaire: your normal body temperature, whether you're sitting right now, whether you've taken any medication. The answers are meant to make the result more accurate.
A few taps later, the app showed me a result without measuring anything. It doesn't use any of the iPhone's sensors. It estimates your temperature from your answers. The App Store screenshots didn't make that clear to me, so it's worth knowing before you pay. If an estimate is what you're after, the app may still be worth a try.
Reading Temperature With the Phone's Own Sensors
In June 2023, researchers at the University of Washington presented FeverPhone, an app that turns a smartphone into a thermometer without any extra accessories. You place the phone's screen on the patient's forehead.
How FeverPhone Works
The app collects data from the phone's touch screen and battery temperature sensors, and a machine learning model turns it into a body temperature estimate. According to its creators, FeverPhone estimates body temperature with an average error of about 0.23 °C. That is within the clinically acceptable error of 0.5 °C.
The model still needs more training data, and as of 2026 the app isn't available in the App Store. The idea is appealing: you only hold the phone to your forehead, and there's no shared thermometer to clean after every use.
Reading Temperature With Accessories or External Sensors
Thermometers for the iPhone connect either through the headphone jack or over Bluetooth.
Wishbone Optical Thermometer
Wishbone plugs into the headphone jack. You connect it, install the companion app and hold the device against the forehead. Its manufacturer describes it as a smart thermometer for quickly and easily taking your child's temperature.
Recent iPhones don't have a headphone jack, so external thermometers increasingly use Bluetooth and send readings to the phone in real time. They differ in how you use them and in accuracy.
Withings Thermometer
Withings Thermo takes the highest temperature reading on the temple. It's a medical-grade product and syncs results automatically with the Health Mate app.
It looks like a classic thermometer, but its 16 infrared sensors take an instant reading from the temporal artery. Among forehead readings, this one is considered to correlate most closely with core body temperature.
Chest-Worn Temperature Monitor
Aidlab is a chest-worn sensor that records skin temperature continuously. A single reading shows one moment, while a continuous record shows how temperature changes through the day and night. During exercise the body heats up noticeably, and a continuous record shows that change across the whole workout.
Aidlab takes its readings from the skin on the chest. It isn't a medical thermometer, so when you need to check for a fever, use one that is.
Apps for Recording Your Readings
Some apps don't measure anything but keep a log of readings from any thermometer. Body Temperature Recorder saves measurements from previous days and draws trend lines, so you can see how your temperature changes over time. You can also note symptoms such as muscle soreness or a sore throat. The Aidlab app lets you add readings manually and save reports as PDFs for later analysis.
Record your own data with Aidlab
Aidlab records ECG, breathing, skin temperature and movement from your chest and sends them to your phone.
