Kicking off its event on Wednesday, Apple (AAPL -0.48%) announced its latest addition to its fast-growing wearables business: a new version of its Apple Watch. The "redesigned and reengineered" Apple Watch Series 4 features a larger display, louder speakers, a next-generation S4 chip, and more.

Here's what you should know about the important new device. 

Apple Watch Series 4

Apple Watch Series 4. Image source: Apple.

The details

Starting at $399, the new Apple Watch Series 4 is a significant upgrade from its predecessor.

One of the most notable upgrades was the watch's first increase in display size. Thanks to narrower bezels, the display is more than 30% larger, pushing closer to the edges of the glass. Apple capitalized on this extra real estate by optimizing the user interface to take advantage of the larger display, enabling content to "be more precise and informative," Apple said in a press release about the new device.

But the watch's new technology on the inside is equally impressive as its form-factor change. Notable new features for the Apple Watch Series 4 include:

  • A new accelerometer and gyroscope that can detect falls.
  • A new S4 chip with a 64-bit dual-core processor, delivering twice the speed of the Series 4
  • The same all-day battery life of its predecessor, despite its improved performance
  • A redesigned Digital Crown that now includes haptic feedback for "a more mechanical and responsive feel..."
  • The addition of yoga and hiking as trackable workout types
  • A 50% louder speaker
A person doing yoga with an Apple Watch

Image source: Apple.

Beyond these features, one topic that received a lot of emphasis during Apple's keynote about the new device was its enhanced heart sensing capabilities. The addition of an electrical heart rate sensor enables the device to administer an FDA-approved electrocardiogram (ECG). The heart rate sensor can also detect signs of atrial fibrillation (AFib).

The new smartwatch, which comes in both 40mm and 44mm sizes, starts at $399. Versions with cellular capabilities start at $499.

Further fortifying its watch lineup is the continued availability of its Apple Watch Series 3 at a new lower price of $279.

A catalyst for an already rapidly growing business

A new Apple Watch with the first major form-factor change since the smartwatch was initially launched in 2015 will help the tech giant capitalize on the extraordinary momentum it is seeing in its wearable business.

In Apple's most recent quarter, watch revenue was up about 45% year over year. In addition, Apple's overall wearables revenue, which includes revenue from Watch, AirPods, and Beats products, exceeded $10 billion over the company's last four quarters. 

Apple isn't wasting any time getting its new watch to customers. Apple Watch Series 4 without cellular capability will be available to order in 26 countries this Friday. The version with cellular capability will be available to order in 16 countries on the same day. By Friday, Sept. 21, both models will be available in stores.