Runkeeper has launched a new Apple Watch app with a functionality that the company's core users -- runners -- have been requesting for a long time: It lets them track their run while leaving their smartphone at home.

There are pros and cons to the new app, which takes advantage of Apple's recently launched Watch OS 2 operating system. It will allow users to track heart rate with the Watch's sensors and view it at a glance as they run, as well as tracking movement with the Watch's built-in accelerometer. Users can also pause their run by swiping or tapping the Watch interface and change their activity type mid-run.

The Watch lacks a GPS of its own, though, so users of the untethered mode won't be able to see a map of their run like they can with the current Runkeeper app. Also, at least at first, the untethered mode will only track average pace on the run, rather than split times or pace charts. Runkeeper hopes to address that in a future update.

Runkeeper has had some challenges adjusting to the changing landscape of the fitness app space in light of recent consolidation. The company laid off 30 percent of its workforce in August as part of a redesign and restructuring that renewed the company's focus on amateur and professional runners as a category.

Runkeeper's app has been around since 2008 and the company has understood the importance of smartwatch integration almost as long as smartwatches have existed: they had one of the first apps for the Pebble Smartwatch back in 2012. At the time, CEO Jason Jacobs even predicted that at some point watches like that would be able to operate independently from the phone.

"What are situations where it is more convenient to check a wristworn computer than to check a phone in your pocket?” Jacobs said at the time. “There are lots of situations where you don’t need a wrist computer, but this happens to be one situation where it does make sense. [Pebble chose Runkeeper as its first app partner] because it a showcase of the value that Pebble is building.”

They were also in a select group of apps that launched with the Samsung Galaxy Gear smartwatch, another pioneer in the space.