Apple has focused on health applications including temperature sensing for menstrual cycle tracking with series eight of the Apple Watch.

Apple Watch Series Eight uses a large, always-on retina display and a crack-resistant front crystal. With all-day 18-hour battery life, it builds on health and safety features such as the ECG app and fall detection by introducing temperature-sensing capabilities, retrospective ovulation estimates, crash detection and international roaming.

The firm has also announced the Apple Watch SE that delivers the core experience, including activity tracking, high and low heart rate notifications, and emergency SOS, as well as the new crash detection feature and a redesigned back case that matches the three classic case finishes.

Both models are powered by Watch OS 9, introducing more customisable watch faces such as Lunar and Metropolitan, an enhanced workout app, sleep stages, AFib history feature and a new medications app.

“We hear from customers how Apple Watch helps them stay connected with loved ones, be more active and live healthier lives,” said Jeff Williams, Apple’s chief operating officer. “Apple Watch Series Eight reinforces our commitment in these areas with the addition of pioneering technology, while Apple Watch SE brings advanced core features at a new starting price. Powered by Watch OS 9, the best smartwatches deliver more capabilities than ever before.”

The menstrual cycle is an important marker of health, and many physicians consider it a vital sign. The Series Eight features temperature-sensing capabilities that give women further insights into their health, designed with the same privacy protections as with all other health data.

Series Eight takes a unique approach to temperature sensing with a two-sensor design, one sensor on the back of the watch, nearest the skin, and another just under the display, reducing bias from the outside environment.

Night-time wrist temperature can be a good indicator of overall body temperature. The sensors in Series Eight sample the wrist temperature during sleep every five seconds and measure changes as small as 0.1˚C.

In the Health app, users can see nightly shifts in baseline temperature, which can be caused by exercise, jet lag or even illness.²

Using the temperature-sensing capabilities, users can receive retrospective ovulation estimates. Knowing when ovulation has occurred can be helpful for family planning, and the watch provides these estimates in the Health app. Temperature sensing also enables improved period predictions. 

Additionally, with iOS 16 and Watch OS 9, all cycle tracking users can receive a notification if their logged cycle history shows a possible deviation, such as irregular, infrequent or prolonged periods, and persistent spotting, which can be symptoms of underlying health conditions.

To enable crash detection, Apple developed a sensor-fusion algorithm that leverages a more powerful gyroscope and accelerometer. To create the algorithm, data were collected from these motion sensors at professional crash test labs with common passenger cars in simulated real-world accidents, including head-on, rear-end, side-impact and rollovers.

In addition to motion data, crash detection uses the barometer, GPS and microphone on iPhone as inputs to detect the unique patterns that can indicate whether a severe crash has taken place. When the watch detects a severe car crash, the device will check in with the user and dial emergency services if they are unresponsive after a ten-second countdown.

Emergency responders will receive the user’s device location, which is also shared with the user’s emergency contacts. When a severe car crash is detected, the emergency services call interface will appear on the watch, as it is most likely to be in closer proximity to the user, while the call is placed through iPhone if it is in range.

A low-power mode can extend battery life to reach up to 36 hours for Series Eight with iPhone present. This mode temporarily disables or limits select sensors and features, including the always-on retina display, workout autostart and heart health notifications.

Users who are diagnosed with AFib can turn on the FDA-cleared AFib history feature and access information including an estimate of how frequently their heart rhythm shows signs of AFib. Users will receive notifications with an estimate from the previous week and also have access to a detailed history in the Health app on iPhone, including lifestyle factors that may influence AFib, such as sleep, alcohol consumption and exercise.

In addition, users can download a PDF from the Health app on iPhone that details the history of their AFib and lifestyle factors, which can easily be shared with doctors and care providers for more informed conversations.

The AFib history feature in Watch OS 9 has received a number of local clearances and approvals from health authorities around the world, and will be available in more than 100 countries and territories, including the USA, Australia, Canada, Europe, Hong Kong, Mexico, South Africa and UK.

The workout app in Watch OS 9 includes in-session views, such as segments, splits and elevation, that offer more precise workout data. Users can also improve their training with workout experiences, including heart rate zones, custom workouts, pacer and, coming later this year, race route.

For triathlons or activities with any sequence of swimming, biking or running, the multisport workout uses autodetection to switch between workouts and records transition times.

Watch OS 9 also brings more data and features to help track how efficiently users run. Running form metrics, including stride length, ground contact time and vertical oscillation, can all be added as metrics on Workout Views.

Sleep tracking in Watch OS 9 provides more insights with the introduction of sleep stages. The watch uses signals from the accelerometer and heart rate sensor to estimate when users are in REM, core or deep sleep. Sleep stage data can be viewed directly in the watch’s Sleep app, and users can view more detailed information in the Health app on iPhone, including interactive sleep stages charts, as well as time asleep alongside heart rate or respiratory rate, in sleep comparison charts.

The new medications experience on Apple Watch and iPhone helps users manage and track their medications, vitamins and supplements, allowing them to create a medications list, set up schedules and reminders, and view information on their medications in the Health app.⁷

When a user’s iPhone is locked with a passcode, touch ID or face ID, all their health and fitness data in the Health app – other than Medical ID – is encrypted. Any Health data backed up to iCloud is encrypted both in transit and on Apple servers. When using iOS and Watch OS with the default two-factor authentication and a passcode, Health app data synced to iCloud are encrypted end-to-end, meaning Apple does not have the key to decrypt the data and therefore cannot read them.