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The Apple Watch can record fluctuations in wrist temperature once you have set up Sleep correctly and worn your Apple Watch for at least four hours per night over five nights. It also works with Cycle Tracking.

Apple added a temperature sensor to the back of the Apple Watch in the 2022 update, but it probably doesn't work how you think. Here's how the sensor works and how to take advantage of it.

How the Apple Watch Temperature Sensor Works

The Apple Watch temperature sensor sits against your wrist and measures small changes in body temperature while you're asleep. Rather than providing you with an exact temperature (like a standard thermometer), you'll instead see fluctuations from your baseline reading.

A close-up view of the optical sensors on the back of the Apple Watch Series 8
Tim Brookes / How-To Geek Tim Brookes / Review Geek Tim Brookes / LifeSavvy

For the feature to work, you'll need to wear your Apple Watch at night for at least 4 hours per night while sleeping for five nights. When you set the feature up, you won't get a reading immediately. Eventually, data will appear in the Health app under Browse > Body Measurements > Wrist Temperature.

Things that can affect your wrist temperature include diet, exercise, alcohol consumption, sleep environment, illness, and the current stage of your menstrual cycle.

Set Up Sleep and Cycle Tracking Use the Apple Watch Thermometer

To take advantage of wrist temperature tracking you'll need to set up Sleep using the Health app on your iPhone. Open Health then navigate to Browse > Sleep and tap "Get Started" to set up sleep tracking. You'll need to enable "Track Sleep with Apple Watch" and use the Sleep Focus for this to work.

Cycle Tracking can also take advantage of the temperature sensor. Set this up using the Health app by navigating to Browse > Cycle Tracking and tapping the "Get Started" button. Apple says that wrist temperature can help you get retrospective ovulation estimates and better period predictions, but that you'll need to wear your watch for at least two cycles in order to gain access to ovulation estimates.

Set up Cycle Tracking on iPhone

You should not rely on Cycle Tracking as a form of birth control since wrist temperature can be impacted by a range of environmental and physiological factors (like the time of year or illness).

Can the Apple Watch Take Your Temperature?

The Apple Watch cannot take your temperature in the traditional sense, it only measures fluctuations in the baseline reading. These can coincide with improved or worsened sleep quality and help predict ovulation or stages of a menstrual cycle. This data cannot be used to diagnose medical conditions, and no temperature reading (for example 99.5ºF) is available.

The Apple Watch may be able to flag health conditions like cardiovascular disease and the Fall Detection feature can call emergency services for you.

Which Apple Watch Models Support Temperature Readings?

Currently, only the Apple Watch Series 8 and the Apple Watch Ultra (2022) can take wrist temperature readings. No models of the Apple Watch SE can take wrist temperature readings at present.

Can You Take Your Temperature with an iPhone?

You can take your temperature with an iPhone but you'll need an accessory to do so. You can use a smart thermometer that connects to your iPhone via Bluetooth and records your body temperature to the iPhone Health app like the Withings Thermo.

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Withings Thermo
Smart Thermometer for iPhone

The Withings Thermo smart thermometer is an FDA-approved no-contact thermometer with 16 infrared sensors that automatically records the temperature of up to eight users.

Alternatively, you can buy a cheap thermometer like the Vicks SpeedRead and manually record any readings to the Apple Health app instead (just as you can with a cheap set of scales and bodyweight readings).

Is the Apple Watch Series 8 Temperature Sensor Worth Upgrading For?

You can read our full review of the Apple Watch Series 8 to see what we think of Apple's first smartwatch with a temperature sensor. For this to be useful you'll need to see the value in tracking your wrist temperature, wear your Apple Watch at night for sleeping, or use Cycle Tracking. Not everyone is going to find temperature tracking useful, so it's probably not worth the upgrade from the Series 7 or Series 6 for most people.

For tighter budgets that still want the convenience of an Apple Watch, there's always the Apple Watch SE (2022). Both models have Crash Detection and the ability to track workouts and physical activity.