How to use the Apple Watch Series 8 temperature sensor

The most important improvement this year Apple Watch Series 8 It is the addition of a new wrist temperature sensor. It’s the first new health sensor to come to Apple Watch since Series 6 Add support for Detection of oxygen levels in the blood. also joins Car accident detection It’s just one of two features that distinguish the new Apple Watch from last year’s model.

However, Apple only allows the new temperature measurement capabilities to be used in two very specific areas of health monitoring, and there is no indication that third-party developers will have any access to them. It’s an interesting contrast Samsung Galaxy Watch 5which also introduced a body temperature sensor that hasn’t yet been used in anything – but for which Samsung has promised to work with developers to build third-party solutions.

Apple Watch Series 7 alongside Samsung Galaxy Watch 5.
Joe Maring / Digital Trends

While the implementations of the new temperature sensor are pretty narrow at this point, there is some hope that Apple can expand the sensor’s capabilities in future WatchOS updates or at least create an API that third-party apps can take advantage of. However, it is important to understand the limitations of the technology that prevent it from being a full-fledged thermometer.

body temperature sensor

When we first heard reports of Apple working on a temperature sensor for the Apple Watch, many hoped it would be advanced enough to run a wide range of health apps. The idea of ​​being able to measure your body temperature on your wrist has opened up many possibilities, from monitoring your overall health and wellness to spotting early signs of infection.

However, it soon became apparent that the human body does not function in such a way as to result in a wrist-based temperature sensor. There is a reason why doctors take your temperature in the mouth, in the ear, or in less comfortable parts of the body. To get a good basal body temperature reading, you need to be reasonably close to your core.

Apple Watch Series 8 appeared.
Joe Maring / Digital Trends

Since the Apple Watch is worn on your wrist, it rules out the possibility of a temperature sensor that can reliably tell if you have a fever. There is simply no way to get an accurate, objective reading of the temperature from one extremity of the body.

It’s also why Apple has avoided calling the new feature a “body temperature” sensor. In most Apple documentation, you’ll see it referred to as either a “wrist temperature sensor” or just a “temperature sensor.” It does not measure your real body temperature, it only measures your wrist temperature.

To achieve this, the Apple Watch Series 8 and Ultra include two separate temperature sensors, one located on the back of the crystal and one just below the display.

Cycle Tracking

However, it turns out that this is enough to turn on some valuable features. Your Apple Watch might not be able to determine your temperature in absolute degrees, but it can create a “normal” core temperature and then record when it’s higher or lower than normal. This lends itself to a feature that is particularly useful for many women.

When Apple introduced the original Apple Watch and its HealthKit frame in 2014, it was It was widely criticized for deleting any features related to women’s reproductive health. The Apple Health app can track even the most obscure vitamin and mineral intakes, yet there’s no place for women to log their menstrual periods.

Apple quickly addressed that the following year with iOS 9 and WatchOS 2, and by the time WatchOS 6 arrived in 2019, the company had made a more serious commitment to women’s health with Dedicated cycle tracking app.

The new app was of great value to women who wanted somewhere to record information about their menstrual cycles. However, it was still Fully manual process. The women had to enter special statistics such as their basal body temperature or the results of an ovulation test. From there, it could predict fertility windows and provide other health insights, but it was only as reliable as the data you put into it.

Temperature sensor on Apple Watch Series 8 ( Apple Watch Ultra) removes much of that guesswork. There is an appreciable change in a woman’s body temperature after ovulation, and the new sensor on the Apple Watch can detect this to provide a retroactive estimate of when ovulation occurred — without having to take manual temperature readings and swipe them into the Cycle Tracking app.

It’s a promising feature for anyone trying to have a baby or simply wanting more insight into their menstrual cycles. However, don’t expect to work right out of the box; Your Apple Watch needs time to get to know you first.

Ovulation Alert on Apple Watch Series 8.

Since the temperature sensor can only detect differences, the Apple Watch must first establish a consistent baseline for determining the normal temperature and when changes usually occur. This means that one needs to constantly wear the Apple Watch for at least two menstrual cycles to collect the necessary data for wrist temperature.

Moreover, to mitigate false readings from daily activities, wrist temperature data is only recorded while you are sleeping. This means that you’ll need to wear your Apple Watch to sleep every night with Sleep Focus enabled for at least two months before you get an ovulation estimate. It also helps if you’ve already accurately logged your periods in the Cycle Tracking app to give your Apple Watch a hint about when you’re most likely to ovulate.

Since the Apple Watch was released less than a month ago, it’s still too early to tell how well this will work in real-world conditions. We hope to start seeing some practical reviews in the near future. Meanwhile, Apple notes that Cycle Tracking should not be used as a form of birth control or as a way to diagnose a health condition without seeing a medical professional.

sleep tracking

With Apple focusing on a temperature sensor to predict a woman’s periods and fertility, it’s easy to dismiss the new feature as completely useless for people who don’t have ovaries.

However, it turns out that the Apple Watch records your wrist temperature data regardless of whether you’ve set up cycle tracking, and it’s happy to provide that data as part of your nighttime sleep tracking results.

If you regularly wear your Apple Watch while sleeping to track sleep, the Series 8 (or Ultra) will measure your wrist temperature while you sleep, taking readings every five seconds to provide an overall temperature for the night. After five nights of sleeping at least four hours each night, you’ll be able to see a chart showing how much your temperature fluctuates from night to night.

Three iPhones displaying wrist temperature readings from Apple Watch Series 8.
Jesse Hollington/Digital Trends

Your wrist temperature data can be found in the iPhone Health app under Body Measurements. It also appears in the Comparisons section with your sleep tracking data. For the first five days of wearing your Apple Watch to sleep, you’ll only see a note saying more data is needed, but once there’s enough data, you’ll get a retrospective estimate that includes those first five days.

Apple doesn’t offer many insights into how to interpret this data, merely suggesting that it can “provide insight into your well-being”. However, it is an interesting metric for those who like to keep track of every detail of their health. It may also be helpful for your doctor in diagnosing a specific medical problem or condition. While Apple notes that fluctuations of up to 1.8 degrees are common, more extreme variations may be a sign that you need to see your doctor.

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