Apple Watch Body Temperature Sensor: What You Need to Know


Measuring body temperature with an Apple Watch was a long-awaited feature. The first patent filed by Apple relative to such a feature dates back to 2014. Since then, analysts have speculated on adding a skin temperature sensor to the Apple Watch Series of the year. The wait is finally over. Last September, Apple announced the release of body temperature capabilities to the Apple Watch Series 8 and its new flagship smartwatch, the Apple Watch Ultra. 

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  • WHY APPLE WATCH ULTRA — Rugged and capable, built to meet the demands of endurance athletes,...
  • EXTREMELY RUGGED, INCREDIBLY CAPABLE — 49mm corrosion-resistant titanium case. Larger Digital...
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Let’s learn how to make the most of these new sensors. Two temperature sensors, one for the skin and another for the environment, are included leading to an unrivaled accuracy of 1/10 of a degree (in Celsius.)

How do the Apple Watch Series 8 and Ultra measure body temperature?

Credit: Apple

For a smartwatch, measuring the skin temperature is complex. First, it is critical to understand the difference between the core and skin temperatures. 

The core body temperature refers to the temperature of the internal organs. It can be estimated by using thermometers that will need to be calibrated and adjusted depending on the location of the measure (mouth, ear, rectum.) Unfortunately, even if these measures provide results closer to the actual core body temperature, they are not accessible with a smartwatch.

All wearable devices will then have to find a compromise: the skin temperature. The main issue with measuring the skin’s temperature is that it will vary greatly depending on the environment and the activities.

To circumvent this variability, Apple and other makers such as Fitbit or Garmin will measure the skin temperature when the body is at rest, namely sleeping.

Fortunately, smartwatches are great for detecting sleep. The Apple Watch Series 8 or Ultra will first establish a baseline of your wrist temperature for five nights. During the following nights, the variations from this baseline will be monitored.

It is easy to understand that the wrist temperature will be different whether you sleep with your hands under or over the blankets or if you prefer to sleep while leaving the window open.

All of these differences in the measurement conditions have an impact on the temperature analysis. To control such variability, Apple did not include just a wrist temperature sensor but also an environmental one. If the wrist temperature sensor detects the skin temperature, the environment one, located on the top of the watch, will analyze the temperature of the air around the device. 

It then becomes possible to control the variability and provides accurate and relevant temperature analyses. 

With an accuracy of 0.1°C, the Apple Watch is probably one of the best wearable devices to follow up on skin temperature evolution.

Credits: Apple

What can you learn from the Apple Watch temperature sensors?

Neither Apple Watch Series 8 nor Ultra are medical devices validated for diagnostics or medical purposes. It doesn’t mean, though, that these features are useless. 

The data will be stored in the Apple Health App under the same privacy rules as any other health data. This way, privacy is ensured.

Even if the watches do not provide instant wrist temperature measurements, measuring the skin temperature trends provide ways to glance at the body temperature to check on your overall health or for women to estimate their ovulation and fertility periods.

The temperature method has been used for decades to estimate fertile periods. According to the Mayo Clinic, the basal body temperature will increase up to 0.3°C following ovulation. This increased body temperature usually lasts a couple of days, corresponding to fertile days.  

Numerous fertility trackers rely on such core principles to help women keep track of their cycles and fertile periods.

Always remember that measuring the skin temperature should not be considered a reliable contraception method and is more indicative than affirmative. 

Credit: Apple

To Conclude

It took time to finally get an Apple Watch with the ability to track skin temperature reliably and efficiently. Still, Apple delivered a much-desired feature with the Series 8 and Ultra.

The accuracy is excellent, and the Apple Watch is one step closer to becoming the ultimate health smartwatch we are all looking for.

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