The bad news is that the Alta HR's sleep tracking can be inconsistent, at least if the pre-release unit I tested is any indication. I was disappointed one morning to find my sleep-tracking chart for the night didn't include any sleep stage information. There was only movement-based data about how long I had been awake, restless and asleep. The company explained that there could be several reasons for the discrepancy. The Alta HR could stop tracking your sleep states if you slept for less than three hours or your battery level is critically low. Also, "your tracker needs to detect your heart rate to estimate your sleep cycles. If you slept in a position that prevented your tracker from getting a consistent heart-rate reading or wore it too loosely, you may see your sleep pattern... instead of sleep stages for the previous night." So that means I have to make sure my arm doesn't shift into an Alta-hindering position all night. Someone should tell Fitbit that is basically impossible.

It's easy enough to make sure you've put on the tracker securely around your wrist before going to bed, but you can't guarantee that your arm doesn't move and nudge the device out of position while you're passed out. I found during my testing that fastening the Alta HR tighter than I normally would helped ensure it didn't budge, but that's slightly uncomfortable and I ultimately didn't find the discomfort worth the information gleaned.

Fitbit should also improve its app's Sleep Insights. When you tap the Benchmarks button on each day's results page, you'll see a shaded bar laid over each sleep stage indicating how long people in your age range and gender typically spent in each zone. It's nice to compare my performance with my peers, but the data otherwise didn't tell me how well I was sleeping. I found myself Googling "How much time a night should I spend in REM sleep?" -- which is information Fitbit could have easily provided within the app.

Based on each night's performance, the app will offer encouragement and education on how to get better sleep. Over time, Fitbit's system is supposed to learn your habits, sleep patterns and activities, and tailor its advice to what it knows you're doing. Since I've only been using the Alta HR for a few days, the tips I've been getting have been generic. Each morning, I get a message within the app that either congratulates me on meeting my seven-hour sleep goal or encourages me to work toward that milestone.

My few complaints aside, I'm satisfied that the Alta HR's new sleep tracking features work as promised, although its accuracy is hard to verify. The rest of the device's functions are the same as they were on the original, except that with the added heart rate sensor you can now monitor your cardio performance while you exercise. As before, the Alta HR sports a "Tap Display," a pseudo-touchscreen that uses an accelerometer to tell when you're jabbing at the panel. It's much less sensitive than a typical touchscreen, and takes some time to get used to, but it's easy enough to activate once you figure it out.

The screen is supposed to wake up from sleep and display your selected watchface when you raise your arm, but this feels sluggish in practice. I have to move my wrist very deliberately before the Alta HR's display will light up. That's more frustrating than having to jab harder at a screen to use the device.

Fitbit continues to promise seven-day battery life for the new Alta, and based on my testing, that's actually a conservative estimate. In the two days since I last plugged in the Alta HR, its battery indicator still says it's fully charged. That's impressive, given that the device has been continuously monitoring my pulse while relaying a handful of alerts from my phone each day. I also check my heart rate at least a few times a day, particularly after climbing up five flights of stairs to my walk-up apartment.

Ultimately, the Alta HR is a successful follow-up to its predecessor, thanks to its new heart rate sensor. It's also one of the more full-featured general-purpose fitness and sleep trackers on the market. Depending on your taste, you might appreciate its bland design too. Those who don't mind a chunkier bracelet should consider the more-capable Charge 2, though. It offers more advanced and precise tracking with its exercise modes and cardio fitness level features, all for the same price as the Alta HR. The Charge 2 will be getting the same sleep stage-tracking feature in April with its next firmware update. But that means it will track the same unverifiable sleep data, which is unlikely to be helpful, regardless of the device it's on.