Apple Watch Series 8 & Ultra temperature sensor, explained

The Apple Watch Series 8 has one important upgrade – a temperature sensor. This can also be found on Ultra. Here’s everything you need to know about this new feature.

A new generation of the company’s smartwatch was announced the other day. In fact we got three new devices this time around. This includes the Series 8 watch, the 2022 version of SE and an Ultra edition as the high-end model.

One of the main upgrades to come on Series 8 and Ultra is a temperature sensing function. This brings the Apple smartwatch one step closer to a must-have health gadget. The company has often stated that this is their goal.


The Apple Watch temperature sensor

The new temperature feature is a bit like the one that can be found on many Fitbit wearables. Rather than tracking core body temperature, it tracks the temperature variations of the skin on your wrist.

Which means, you don’t get absolute values. Instead a core baseline will be established. And then, you will get a chart and stats showing how much you deviate from your norm. This can act as a decent indicator of changes in your core body temperature.

Skin temperature measurements are only taken at night, while you sleep. It would not make much sense to do this throughtout the day as the readings might fluctuate quite a bit depending on the type of activity you are engaged in.

At night, the temperature sensor kicks in quite often – every 5 seconds. Apple says the tech is very sensitive and that it can pick up changes in temperature as small as 0.1 degrees Celsius. Nightly shifts can be an indicator of illness, or they might stem from exercise, jet lag and similar.

In the morning you can see the nightly shifts from your baseline value. In addition to a one day overview, you can group the data by week, month and six months.

Apple Watch temperature sensor

To ensure accuracy, Apple has built two temperature sensors in the watch. One sits next to the heart rate sensor on the underside of the watch. The other one is just above the screen.

The first is used to capture skin temperature, the other one is utilized to reduce bias from the outside environment. That one is also used to measure the temperature of the water when diving.


Temperature info allows for better cycle tracking

Apple is going a step further this data and using it to enhance cycle tracking – an important marker of health. That feature has been around for some three years now, but with temperature info it is better than ever.

Temperature taking is useful for those who ovulate, as it indicates ovulation via biphasic shift. For most people their temperature is lower in the first part of their cycle – usually between 96°and 98° Fahrenheit. This rises when you ovulate – about fourt-tenths to one degree higher than your typical temperature.

The info gathered from the sensor allows for retrospective ovulation estimates in the Health App, i.e. when ovulation has occured. What’s more users will get improved period predictions and detailed views of their cycles. Plus there’s the addition of notifications if the logged cycle history shows a possible deviation.

All of this can be useful for family planning. Temperature can be used as a way to predict fertility.

Essential readingTop fitness trackers and health gadgets

As you’d expect, privacy protection is at the core of this new feature. The data is encrypted on your device and is only accessible to a person with the passcode or correct authentication. Apple doesn’t have the key to decrypt this data.

As mentioned temperature tracking and improved cycle tracking is only available on the Series 8 Watch and Ultra. Both of these are available on Apple’s website and Amazon (check Series 8 price, check Ultra price) and will ship later this month.

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