Apple Watch Series 3 guide: Everything you need to know

The Apple Watch Series 3 is official, and just as expected the new smartwatch comes with LTE built in, letting you keep a connection when away from your phone.

The Series 3 is almost the same size as Series 2, but inside is a zippier new processor that Apple says will be faster and more power efficient. But the big thing here is the cellular connection, and the good news is that you won't have to get new digits to use it, as the Watch will share your current phone number with its built-in SIM.

The verdict is in: Apple Watch Series 3 review

There are a few other improvements too, such as a barometric altimeter for tracking your elevation, which means the Watch now also tracks stairs climbed. It's swimproof, as expected, and lands running the flashy new watchOS 4 software.

Read on for everything you need to know about the Apple Watch Series 3.

Apple Watch Series 3: Everything LTE

Alongside a cheaper, GPS-only Apple Watch Series 3 is the LTE version, which boasts its own cellular connection. The new Apple Watch uses an eSIM, which means you don't have to insert a SIM card, and also allows you to share your number with your iPhone, depending on your carrier.

Read more: LTE smartwatches explained

But don't think that means it doesn't cost money. You'll still need to sign a deal with a carrier to get LTE connectivity – despite sharing a telephone number with your smartphone.

One caveat to LTE connectivity. T-Mobile will not be providing LTE speeds for your Series 3. Instead, you'll only be able to achieve 512kb/s, which is closer in speed to 3G than LTE. This is because T-Mobile's ONE plan limits all wearables and tethered devices to 512kb/s and, thus far, it isn't making any exception for Apple.

So what does it do? Apple has revealed that this will enable users to take/make calls, along with getting all your other notifications. You'll also be able to access Apple Music directly from the watch, so you can head out for a workout sans iPhone and still be able to stream tunes.

Availability for Apple Watch Series 3 with LTE carrier plans is pretty widespread, but far from worldwide. From launch you'll be able to find a Watch-specific tariff in Australia, Canada, China, France, Germany, Japan, Puerto Rico, Switzerland, the UK and the US.

In the US AT&T, T-Mobile and Verizon have announced pricing – it'll cost you $10 a month, which is comparable to other wearable devices. While AT&T isn't offering any deals, Verizon and T-Mobile customers will get three free months of LTE Apple Watch service. Spring will also carry the LTE Apple Watch, but hasn't announced pricing yet, though it's a safe bet it will also offer $10 a month.

Over in the UK, EE will be the sole carrier of the LTE-enabled Watch, and will add the Watch to your plan for £5 a month.

Apple Watch Series 3: The specs

As you'd expect, the Apple Watch Series 3 comes with a new chip under the hood. The custom designed W2 chip offers a 70% boost in raw performance over the Series 2, while delivering "all day battery life", according to Apple. In terms of real-world use, that means about 18 hours, which is about the same as we get with the Series 2.

Then there's LTE. As we've mentioned the cellular version features an eSIM, which Apple says is one-hundreth of the size of a nano-SIM card, and has enabled the company to incorporate the technology while only increasing the depth by 0.25mm. That's also been implemented by using the screen as a giant antenna.

The new W2 chip also enables Siri to talk back to you. It may have surprised some non-Apple Watch aficionados that Siri was mute on the Series 2, but this now offers a comparable experience with your iPhone. What's more, Apple says the new chip is 50% more power efficient than the last generation – and it will need to be.

LTE, of course, will drain that battery a quicker. For example, Apple says you can expect an hour of talk time via LTE and three hours of talk time when connected to an iPhone. Working out outdoors gets you four hours with LTE and GPS, five hours with GPS alone and 10 hours with neither. There's no difference when streaming Apple Music though.

There's a new sensor in town, too. The Apple Watch Series 3 is the first to incorporate an barometric altimeter – a pressure sensor to you and I. That means the Series 3 can track stairs climbed to help you close your rings, but will also allow for tracking of snowboarding and skiing for gnarly dudes and dudettes.

At only a hair thicker than the Series 2, Apple's done a decent job of keeping the case size contained. Otherwise it's exactly the same form factor, though the LTE model will come with a red accent on the digital crown to distinguish it from the less expensive, non-LTE version. Oh, and if you're looking at the Stainless Steel or Ceramic models, you should know those will only be available with LTE.

The new Watch comes in some new colours too – a Blush Gold and Ceramic Gray – while Apple is offering some new Nike+ models and Hermès bands.

New watchOS 4 details

Though we've been playing with a beta version of watchOS 4 for some time, Apple announced yet more features focused around health coming to the software in time for Series 3.

Along with a new heart beat complication and a better graph on the Watch for seeing your heart rate through the day, Apple is putting more focus on wellness, something we've seen more and more from other companies like Garmin and Fitbit recently.

There will be a resting heart rate feature, which has been a notable omission on the Apple Watch until now, being a great measure of improving fitness. It will also focus on recovery after workouts, which until now has been the kind of detail reserved for specialist (and costly) fitness devices.

Read this: Atrial fibrillation explained

And there's more to come. A new feature will alert users if their heart rate is elevated unduly, which moves the Apple Watch into the realms of a consumer health device. And Apple has confirmed it is working with Stanford and American Well to track atrial fibrillation, a condition that causes irregular heartbeats. A new app called Apple Heart Study will be the first phase of that, which the company will release on the US App Store in October.

Apple Watch Series 3: New Nike+ designs

Of course Apple isn't forgetting about the Nike+, and will launch a new Series 3 version of its Nike-branded Apple Watch, complete with new designs.

There's also set to be a new version of the Nike+ Run Club app which is baked into the Nike+ Apple Watch, which will come with a new audio coaching feature. Included in that will be some audio-guided runs from Nike's stable of fitness experts; meanwhile friends will be able to send audio cheers to you while you're in the middle of a workout.

Apple is also introducing new a new Nike sport band and a new sport loop band for the Series 3, which will be available in either black or platinum. The Nike+ edition won't launch day and date with the other Series 3 models though – you'll have to wait until 5 October for it.

Apple Watch Series 3 vs Series 2

The big question many of you will be asking is how the Series 3 compares to the Series 2. Until we can test them side by side, we can only go from what's on paper, and beyond LTE there isn't a huge amount of difference.

One of the biggies is that the Series 3 is faster, with Apple touting that 70% performance boost, while the barometric altimeter means you'll only get the elevation tracking on the new models.

In terms of size, you're pretty much looking at the same smartwatch. Apple says the glass on the back of Series 3 is 0.25mm thicker – about two sheets of paper – which means it will be even less noticeable than the case bump-up between Series 1 and Series 2. The only other design difference is the red accent crown on the LTE version, while the non-LTE Series 3 is indistinguishable from its predecessor.

Apple Watch Series 3: Release date

The Series 3 will be priced at , while Apple is offering the non-LTE version for . In the US, it'll be available for all four major carriers while it'll be available with EE in the UK. It's also keeping the Series 1 alive alongside for , but dropping the Series 2. The new Apple Watch Series 3 will be available to wrap around your wrist on 22 September.