Apple just unveiled its latest smartwatch, the Apple Watch Series 3 - here's everything you need to know

Apple just revealed the newest version of its smartwatch: the Apple Watch Series 3.

At its annual event on Tuesday to unveil its latest hardware products, Apple launched its third-generation Apple Watch - the first one with cellular built-in. The watch can make and receive calls, allowing you to leave your phone at home. The Series 3 watch will have the same number as your iPhone.

"Now you have the freedom to go anywhere with just your Apple Watch," said Apple COO Jeff Williams. "This has been our vision since the very beginning."

The watch will be available to order on September 15 date and will start at $329 - the watch will cost $399 with cellular built in. The watch will be available on September 22.

The new watch comes in three colors: A new gold aluminum finish, silver, and space gray. The new Apple Watch Edition, which has a ceramic case, will come in a new gray finish (the previous version only came in white).

Here are the features of Apple Watch Series 3:

• Up to 18 hours of battery life
• The ability to stream up to 40 million songs thanks to the cellular connection
• A new dual-core processor
• Apple-designed custom W2 chip
• A barometric altimeter

The Apple Watch Series 3 will run WatchOS 4, Apple's smartwatch operating system. WatchOS 4 will have Siri built in, will be able to handle person to person payments using Apple Pay, smart activity coaching, a redesigned workout app, and more. WatchOS 4 will arrive on September 19.

Apple's most recent smartwatch, the Apple Watch Series 2, was released a year ago and featured a faster processor, GPS tracking, and the ability to wear it while swimming.

The Apple Watch Series 1 and 2, which are still available to buy, both come in rose gold, space gray, and gold. The Series 1 starts a $269, while the Series 2 starts at $369. The Series 2 also comes in stainless steel and space black, which start at $549.

Apple's premium smartwatch, the Apple Watch Edition, has a white ceramic case and starts at $1,249.

Apple says sales of the Apple Watch grew 50% last quarter compared to previous year, and is now "the No. 1 watch in the world." While Apple doesn't release official sales figures, analysts estimate that Apple shipped 4.6 million Apple Watches during the 2016 holiday quarter.