The Apple Watch is inching toward becoming a medical device

CUPERTINO, Calif. (AP) — Apple is trying to turn its smartwatch from a niche gadget into a lifeline to better health by slowly evolving it into a medical device.

In its fourth incarnation, called Series 4 and due out later this month, the Apple Watch will add features that allow it to take high-quality heart readings and detect falls. It's part of Apple's long-in-the-making strategy to give people a distinct reason to buy a wrist gadget that largely does things smartphones already do.

Since the Apple Watch launched in April 2015 , most people haven't figured out why they need to buy one.

Apple doesn't release sales figures, but estimates from two analysts suggest the company shipped roughly 18 million of the gadgets in 2017. Apple sold almost 12 times as many iPhones – 216 million – that year. Apple shipped another 7.3 million Apple Watches during the first half of this year, according to Canalys Research, compared with more than 93 million iPhones.

Worldwide, about 48 million smartwatches are expected to be sold this year, compared with nearly 1.9 billion phones, according to the research firm Gartner.

Apple CEO Tim Cook has long aimed to emphasize the health- and fitness-tracking abilities of the smartwatch. The original version featured a heart-rate sensor that fed data into fitness and workout apps so they could suggest new goals and offer digital "rewards" for fitness accomplishments.

Two years later, Apple called its watch "the ultimate device for a healthy life," emphasizing water resistance for swimmers and built-in GPS for tracking runs or cycling workouts. In February, the company announced that the watch would track skiing and snowboarding runs, including data on speed and vertical descent.

The latest version, unveiled Wednesday, is pushing the health envelope even further – in particular by taking electrocardiograms, or EKGs, on the device, a feature given clearance by the U.S. Food and Drug Administration, Apple said. The watch will also monitor for irregular heartbeats and can detect when the wearer has fallen, the company said.