CUPERTINO, Calif.—At Apple's headquarters today, the company announced a new Apple Watch Series 3, which will have standalone LTE service. This feature breaks the necessary connection between the wearable and an iPhone, allowing it to receive messages, download apps, stream music, and connect to the Internet without help.

The new Apple Watch with Cellular, as it's called, will be available on September 22 in 10 countries and will start at $399/£399. A separate version without LTE service will be more widely available and will start at $329/£329. The older Apple Watch Series 1 will now start at $249/£249, while Apple looks to be phasing out the Series 2. Pre-orders for the new models will start on September 15.

Apple says the Watch with Cellular will work with Verizon, AT&T, Sprint, and T-Mobile in the US, and exclusively on the EE network in the UK at launch. All four major US carriers say it'll cost $10 a month to add the device to an existing mobile plan, though that price will typically cost $5 more a month for those who don't enroll in auto-pay billing. Each one also says they will make that connection free for the first three months. UK EE customers will be charged £5 on top of an existing plan.

Standalone LTE service was the primary rumor swirling about the Apple Watch before today's event. Apple released the Series 2 smartwatch last year, which updated the device with onboard GPS and a water-resistance mechanism for swim tracking. Those features will remain on the new models.

Apple says the device itself connects through eSIM and runs on a new dual-core processor called the S3, which the company claims will give the Watch Series 3 70 percent more performance than the Series 2. Apple says this will let users hear Siri through the Watch's speakers. The company says that it has integrated a new wireless chip called the W2 to beef up Bluetooth and Wi-Fi performance as well, and a barometric altimeter has been added for tracking elevation.

Notably, despite the new LTE (and UMTS) radio, Apple says the Watch Series 3 is close to the same size as its predecessor, save for a back crystal that's 0.25 millimeters chunkier than before. Apple said it achieve this by using the Watch's display as the LTE antenna. Outside of a red digital crown piece on the LTE model, though, the device appears to look just about identical to the Series 2.

As previously rumored, the new Apple Watch will be able to share the same phone number as a user’s iPhone. This is done through number sharing solutions from carriers such as AT&T's NumberSync or T-Mobile's Digits plan.

Battery life has presented the biggest issue in implementing LTE connectivity on wearables. Most smartwatches have abysmal battery life to begin with, and LTE has only sucked up energy faster on wearables like Samsung's Gear S3 and LG's Watch Sport. Apple, for its part, says the Watch Series 3 will get up to 18 hours of juice with "a mix of LTE, Bluetooth, and Wi-Fi." By comparison, the Apple Watch Series 2 lasted about two days on a single charge. Beyond that, Apple's Battery Information page says that the new device will get just one hour of talk time when used strictly over LTE.

Naturally, the new Apple Watch will come with a new version of WatchOS. That update, called WatchOS 4, was mainly detailed at Apple’s WWDC developer conference in June and includes new watch faces—including one focused on the company’s Siri voice assistant—as well as a few visual tweaks and updates to the company’s activity tracking apps. Apple also detailed new features related to heart monitoring at its event on Tuesday and said the Watch would be able to stream from Apple Music starting next month.

Apple says the Series 3 Watch will come in silver, space gray, and a new gold casing. The usual variety of bands will be available, too, including a new "Sport Loop" option that appears to be thinner and more lightweight than usual.

The market for wearables, and smartwatches in particular, is still nowhere close to the level of the smartphone, but the Apple Watch has been one of the bigger fishes in that small pond. According to recent data from research firm IDC, Apple Watch sales are steadily increasing, and Apple only trails Chinese firm Xiaomi, which mainly sells lower-cost devices, in market share.

Edit: Updated with pricing from all four major mobile carriers in the US.