At CES in Las Vegas on Tuesday, Fitbit unveiled a smartly designed smartwatch/fitness tracker combination called Fitbit Blaze.

At $199, with a color touchscreen and 5 days of battery life, it’s a device that’s rich in software and hardware features for fitness, tracking runs, workouts, yoga sessions, and other activity with rich detail.

The Blaze follows last year’s release of Fitbit’s Surge and Charge trackers, which added heart-rate tracking to Fitbit’s lineup, and took it into a realm of tracking more vigorous workouts including runs and weightlifting, not just steps.

In so doing, Fitbit is throwing down a challenge to Apple, which has touted the fitness features of the Apple Watch, and other makers of fitness trackers like Runtastic and now Under Armour, who have yet to put a dent in Fitbit’s dominance of the market.

One of the most interesting features for me was the inclusion of basic workouts from FitStar, an app maker Fitbit acquired last year. While it doesn’t include the full range of FitStar’s customized workouts, the FitStar app on the Fitbit Blaze could help people do quick hotel-room or office workouts when they don’t have access to a gym.

I actually think Fitbit and FitStar got that integration backwards: I would have liked to have seen FitStar use heart-rate and activity data from the Blaze to do deeper personalization on its workouts. The Blaze tracks resting heart rate, a measure of overall health that can be useful in, say, telling you whether you should skip a workout or go all-out.

What Fitbit Has Yet To Work Out: An App Store

And that points out the bigger flaw in Blaze—and Fitbit’s other trackers, for that matter. The only software they can run is software that Fitbit puts on there. While they’re excellent devices, and sell exceedingly well, they’re limited to what Fitbit’s engineers can come up with (and what they have time to build).

Fitbit has an excellent sense of what people want in a fitness tracker, as evidenced by the company’s still-leading market share, which the Apple Watch has yet to threaten. So perhaps the lack of access to the Blaze’s innards for developers to build apps won’t be a problem. Arguably, supporting third-party developers would take away already-scarce engineering resources.

Intriguingly, Fitbit is hiring a product manager for its API, seeking candidates with firmware experience, as well as a firmware engineer who will work closely with the API team. These openings suggest that more access to Fitbit’s devices is coming.

Ultimately, I think Fitbit will have to open up its hardware, much as it has already done with its well-used software API. Those same developers who want to tap into Fitbit’s fitness data will want to do the same with its hardware—especially if the Blaze proves as good-looking and capable as it appears on first glance.

Product photos courtesy of Fitbit; photo of James Park by Owen Thomas for ReadWrite