The new Apple Watch will be launched with an edge-to-edge screen and ECG support, the company has announced at an event in San Francisco.

The Apple Watch Series 4 will be available to order from Friday 14 September. Pricing starts at $399 (£399) for the GPS version and $499 (£499) for a version with LTE connectivity. Series 3 Watches will see a price cut to $279 (£279).

The larger model now comes with a 44mm screen, up from 42mm, and the smaller version’s previously 38mm screen is now 40mm.

Both devices are the same physical size as the watches they replace, and will be available with LTE connectivity as an optional extra.

Alongside the screen upgrade, the watches are also receiving improved health-tracking abilities, augmenting the light-based heart monitor found in earlier models with a new ECG-based system, which is generally more accurate – particularly when used on dark or tattooed skin. The ECG feature will initially only be available in the US.

The watch will also be able to detect when the wearer is falling, a feature Apple say could help in emergencies. Apple’s chief operating officer Jeff Williams, who announced the new models, described them as an “intelligent guardian for your health.”

Williams also said the watch’s battery life would be the same as the previous edition of the Apple Watch, at 18 hours.

The new Apple Watch will come with watchOS 5, the latest version of the company’s operating system for smartwatches, which will be available from 17 September. The software features updates for the workout tool on the watch, the ability to listen to podcasts while exercising, and a raft of changes to notifications to try to limit the information overload wearers can suffer.