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How does the Apple Watch work? Activity tracking, calorie counting and more explained

We pull apart the Apple Watch to see how it tracks your daily activities, including counting steps, measuring your calorie burn, monitoring how often you stand and tracking your sleep. Here's how the Apple Watch actually works.

The Apple Watch is a pretty smart bit of kit, packing all kinds of sensors and trackers which allow it to figure out whatever you're up to.

Of course, there are differences between the two different models, or 'Series' as Apple calls them. The Apple Watch Series 1 (the original wearable) doesn’t have the GPS capabilities of the Series 2 Apple Watch, but they both offer plenty of functionality. From tracking runs to playing music to controlling your smarthome with voice commands alone, the Apple Watch is a device which makes life much easier.

Here's how the Watch keeps tabs on everything you do and communicates with your iPhone, to record information and more besides.

How does the Apple Watch communicate with my iPhone?

The connection between iPhone and watch is a simple one as it uses the popular Bluetooth radio signal system. This allows for two-way communication, with enough bandwidth to transfer images, music, voice data and more between the two devices.

When your Apple watch communicates directly with the internet it uses Wi-Fi, meaning it can still work online even without your phone nearby and connected.

How does the Apple Watch track sleep?

Thanks to a selection of motion sensors including a gyroscope and accelerometer, the Apple Watch can track your sleep with reasonable accuracy.

The Apple Watch is able to detect deep sleep through lack of motion and then, as you move about in bed, the device can determine when you’re in lighter stages of sleep or fully awake. Ultimately you’re left with a readout on how well you slept.

The results on offer varies depending on what app you use with the likes of AutoSleep, Sleep Tracker and Sleep Cycle all giving in-depth feedback. Apps like Sleep Cycle Alarm Clock even wake you just as you’re entering a period of light sleep, so you feel refreshed enough to start the day.

Be warned of course, tracking your sleep means no charging overnight. Our top tip is to pop your Apple Watch on charge first thing in the morning as you get out of bed, and it should be good to go again by the time you leave the house.

How does the Apple Watch track your activity?

Once again, those motion sensors are hard at work during the day to keep track of your activity. That doesn’t just mean step counting though. The Apple Watch with its built-in Activity app tracks how often you've been standing, using a ring readout on the display. This also reveals how much you've been moving, to help keep you from being too stagnant, plus a workout ring for training tracking at a glance.

When it comes to exercise, you can use specific training apps or the Workout app. In the case of the Series 2 Watch, you even have GPS built-in, meaning you can track a run or cycle distance accurately, without carrying your iPhone. Choose from 12 workout types including swimming, outdoor cycling, indoor elliptical and more.

How does the Apple Watch count steps?

You guessed it, the Watch uses the motion sensors to detect steps accurately. Apple's wearable can even learn and track your steps more accurately over time, as your movements become more predictable. The result is a comprehensive read-out of the times you were in motion, be it walk or run, for the entire day.

The Watch can track steps even as they vary in stride between walking and running. Apple's device can also detect when you're powering up and down stairs, thanks to those motion sensors combined with smart algorithms.

How does the Apple Watch count calories?

The Apple Watch is just as smart when it comes to counting calories, as it uses both motion and heart rate to calculate a more accurate figure.

The more you wear your Apple Watch, the smarter and more accurate it becomes. The wrist rocket can learn how your heart rate varies depending on your activity levels, to refine that counter as time goes on. So this smart watch can take into account your number of steps, how long you've spent standing and performing actual exercise, to give a more accurate figure of your overall calorie burn.

How does the Apple Watch know you're standing?

Standing and sitting are measured using similar motion sensor smarts. Inactivity suggests sitting, of course, although that's not always accurate - you may be propped up at the bar, for instance. Therefore, the Apple Watch also takes into account the way your wrist moves, say when typing at a desk. Heart rate is also a factor here, as when you stand there is a sudden rush of blood as your body fires up for movement.

The result should be a more accurate measure of movement to stand. Since you also get move alerts throughout the day with Apple Watch, this can help to predict when you stand - since it’s combined with your daily movement routines.

However, note that standing desks tend to flummox the Apple Watch. All of that static motion combined with constant typing makes it think you're sat down.

How does the Apple Watch measure heart rate?

The Apple Watch uses an optical heart rate monitor to measure your heart rate. This works by shining a light onto your skin, from the underside of the device. As your blood moves through your veins, that light is blocked, which is detected by the Watch. The result is an impressively accurate measure of pulse rate.

Check out our Apple Watch hub for everything you need to know about the Apple Watch. Including:

Apple Watch tips, tricks and best hidden features

Which Apple Watch is right for me?

When is the Apple Watch Series 3 going to be released?

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