Three years after Pebble started selling its original Kickstarter-funded smartwatch, the Redwood City, California-based startup is rolling out a successor. The new Pebble 2 has some aesthetic improvements, but the most notable new feature is the Pebble 2's ability to track heart rate. In fact, the Pebble Time 2, another new smartwatch, will also feature heart rate sensors, and Pebble says they'll be included on all future Pebble watches.

Pebble says it decided to include heart rate tracking because the company believes fitness tracking has become the third pillar of smartwatch functionality, alongside notifications and basic communications. But it's also an acknowledgement on the part of Pebble that it will need to keep innovating on its relatively simplistic smartwatches if it plans to continue to compete with much bigger companies that are making wearables.

The new Pebble 2 smartwatch is thinner and lighter than the original Pebble. It has the same black-and-white display, but with a Corning Gorilla Glass coating instead of the plastic coating on the previous Pebble. And, in addition to the optical heart rate sensors, the Pebble 2 has a built-in microphone — something the original Pebble didn't have.

In addition to that watch, the company is also introducing the Pebble Time 2, which combines features of the Pebble Time and Pebble Time Steel smartwatches. (Pebble will phase out those two previous watches; it's just the Pebble Time 2 going forward.) The Pebble Time 2 is made of steel and has a noticeably smaller bezel than the previous watch, which means its color display has more than 50 percent more viewing area. Like the Pebble 2, the Pebble Time 2 is coated in scratch-resistant glass, is water-resistant up to 30 meters, has a built-in microphone, and includes new heart rate sensors.

Per usual, battery life is one of Pebble's standout features. The new Pebble 2 has a battery life estimate of a week, while the Pebble Time 2 should last around 10 days — even with the inclusion of heart rate sensors and a microphone.

And finally, the new Pebbles will include a framework for apps called Actions, which Pebble has designed with quick access to core app functions in mind. Press on the top right physical button on the watch, and it will bring you to an Uber shortcut, or a texting shortcut, or whatever other quick actions developers might create for their apps on Pebble's OS.

Pebble has sold 1.8 million smartwatches to date

Both the new Pebble 2 and the Pebble Time 2 go on sale on Kickstarter today. The Pebble 2 costs $99 and is expected to ship in September; Pebble Time 2 is more expensive at $169, and Pebble says it should ship in November.

The refined look of both the Pebble 2 and the Pebble Time 2 are nice enough, and the heart rate sensors are a welcome addition. But it's somewhat of a me-too move for Pebble, which admits it was late to take health and fitness tracking seriously. While Pebble watches have run simplified versions of third-party apps like Jawbone and Misfit for a while now, it only just launched its own health-tracking app this past December.

And while Pebble has an enthusiastic user base, some of whom have backed Pebble on Kickstarter from the very beginning, the company has only sold 1.8 million watches to date, according to Pebble founder and chief executive Eric Migicovsky. That number pales in comparison to the estimated number of Apple Watches, Xiaomi wearbles, and Fitbits sold. And the most popular Pebble has been the original one.

When I asked him about this level of competition in the wearables space, Migicovsky pointed out that 1.8 million is still greater than the reported number of Android Wear watches sold. "Pebble is affordable, it's fun, and it doesn't take itself too seriously," Migicovsky said, adding that customers often buy more than one Pebble because they're accessible. "We're pretty comfortable in that space."

Pebble is also introducing its first non-smartwatch gadget, the Core, which you can read more about here.