Making an accurate wristband heart rate monitor, let alone one that's also comfortable and stylish, is challenging. Fitbit's latest attempt to strike that balance is the $150 Alta HR. A near mirror-image of the original Alta, the Alta HR is an updated model with slight design differences, improved sleep-tracking features, and a tiny optical heart-rate monitor inside of it.

The Alta HR is quite similar to Fitbit's currently available Charge 2, but the Alta HR places more emphasis on the combination of a slim design and an accurate heart-rate monitor. Fitbit is banking on that combination encouraging users to wear a device all day and all night long. The Alta HR is proof that you can have a device that works as hard as you do without being ostentatious and without much sacrifice.

Design: Familiar, yet more thoughtful

The Alta HR looks nearly identical to the original Alta, and its symmetry is one of its biggest selling points. Fitbit managed to shrink the internal tech by 25 percent to make room for an optical heart rate monitor inside the Alta's svelte frame. Coming in small, large, and extra large sizes, all Alta HR models are just 0.61 inches (1.6 cm) wide. That makes the device .23 inches (0.6 cm) thinner than the $150 Fitbit Charge 2. It also has the same tappable display as the original device and the Charge 2, but the HR responds to taps much better than the Alta did. There are no physical buttons on the Alta HR, so you can only tap the display to scroll through activity data screens. Waking the Alta HR's display rarely took more than one tap, whereas the Alta often needed three to five taps to wake up at all.

The most noticeable difference is in the Alta HR's bands: instead of the Alta's snap closure, the Alta HR has a more watch-like band made of flexible elastomer and features a simple, semi-flexible buckle. Not only does the new band make the device easier to strap on, it also lets you get the perfect fit for measuring heart rate. As with any wrist-bound optical heart-rate monitor, the one in the Alta HR can interfere with blood flow and provide an inaccurate pulse reading if the device is strapped too tightly. On the flip side, it shouldn't be so loose that air gets between the wrist and the monitor. While the original Alta's snap closure is perfectly adequate for that device, the more secure band on the Alta HR is necessary.

The band is interchangeable, just like on the original Alta. Fitbit has a bunch of styles available in leather, metal, and, of course, elastomer, which is ideal for exercise. Although the Alta HR might not be water-resistant enough to swim with (the Flex 2 is still the only Fitbit tracker with that perk), it is comfortable to wear all day and while you're sleeping. Since the new sleep features that are supposed to help you sleep better require the heart-rate monitor, the Alta HR needs to be easy to sleep with around your wrist. I slept with the device on for a few weeks, strapped as I typically would to ensure proper heart-rate measurement, and it never bothered me. I slept mostly with the sport band on the Alta HR and a few times with a leather band; I would wager the only uncomfortable band to sleep with is the bracelet-like metal band.

Thanks to its smaller internals, the Alta HR is estimated to last seven days on a single charge. That's with continuous heart-rate monitoring and sleep tracking, making it an extremely competitive device in terms of battery life. On the seventh consecutive day of wearing the Alta HR, I received a notification in the app that the battery was low. I typically tracked one or two workouts per day and wore the device to bed each night. Even with all that use, the Alta HR lasted over a week before it needed more juice.

Valentina Palladino

Valentina Palladino

Valentina Palladino

Valentina Palladino

An improved band makes it easier to fasten around your wrist tightly.

Features: Constantly learning more about you

The Alta HR has nearly all the same features as the Charge 2, the most important of which are daily activity and sleep tracking, continuous heart-rate monitoring, and auto-recognition of exercises. From the moment you strap on the Alta HR, it tracks your steps, calories, distance, and heart rate, and it will continue to monitor movement and pulse while you sleep. The heart-rate monitor enhances some of these features: Fitbit claims the caloric-expenditure estimates will be more accurate than before thanks to the heart-rate monitor, and the monitor feeds data into the new Sleep Stages and Sleep Insight features that help you get a better night of shut-eye.

Thankfully, the heart-rate monitor is pretty accurate. When I tested it against the Polar H7 heart-rate monitoring chest strap, the Alta HR typically hovered within three to five BPMs of the H7's measurement. However, the Alta HR took a few more seconds to level off at a medium-intensity pulse after being at a high-intensity pulse for a few minutes. The H7 chest strap's readings fell steadily from the 170s to the 130s, but the Alta HR took a few more seconds to level off at the new, lower heart rate.

Actually seeing your heart rate on the Alta HR during a workout is a little frustrating. You must tap the display to go to the heart-rate screen to see your real-time measurement, and that's easier said than done when you're in the middle of a 5K run. The only way to make this easier is to customize the order of your Alta HR's screens in the Fitbit app and set the heart-rate screen to be the first one that pops up when you turn your wrist upward.

One of the differences between the Charge 2 and the Alta HR is that you cannot access sport profiles on the new device. You can save a few sport profiles to the Charge 2, allowing you to easily start a recorded workout from the device. But with the Alta HR, you must rely on the exercise auto-recognition feature or wait until you're done exercising and manually log workouts in the mobile app. Auto-recognition and recording is one of Fitbit's best features: the Alta HR will automatically record walk, run, elliptical, and bike workouts, as well as "sports" (a good generic category if you do a particular sport regularly) and "aerobic" workouts (another good category for HIIT sessions and the like) that you do for more than 10 minutes. This time threshold can be changed in the app, but the least amount of time needed to recognize and record an activity is 10 minutes. I only logged one session manually in the app while I used the Alta HR (it was a 10-minute stair-stepper session that I categorize as an aerobic exercise). Otherwise, the device picked up every workout I did without my help.

The other two differences between the Charge 2 and the Alta HR is that the latter doesn't have guided breathing sessions, nor does it have a connected GPS feature. The Charge 2's guided breathing feature uses the display to lead you through a deep breathing session that helps lower your heart rate and keep you relaxed. It's not a necessary feature—most fitness trackers don't have it—but guided breathing might be good for your mental health if you're constantly feeling stressed or anxious. The connected GPS feature lets you map outdoor running routes when you take the Charge 2 on a run with your smartphone. The lack of this feature might deter runners from buying the Alta HR: if you're accustomed to running outside and want to review a route map at the end of each session, you can't get that with the Alta HR.

Measuring heart rate while you sleep

We'll discuss the Alta HR's improved sleep features in the app section, but they are improved primarily because of the heart-rate monitor. Not only does the monitor work all day, but it also measures your pulse throughout the night and your resting heart rate before you wake up. That continuous nighttime heart rate, plus heart-rate variability data and the accelerometer's movement information, gives you a better picture of your night's sleep. Most other devices use movement data alone to judge if you've slept well or not (if you move too much, your session is automatically considered a bad night's sleep), so adding heart-rate information makes the information more clear and accurate. Heart rate and heart-rate variability also lets the Alta HR estimate the amount of time you spend in light, deep, and REM sleep, as well as the periods when you're awake at night. Before the introduction of Sleep Stages, Fitbit devices could only estimate light, deep, and awake times.

The Alta HR also has a number of alert features that are standard for nearly every Fitbit device. It receives text, call, and calendar alerts from your smartphone, which isn't as many notifications as the $150 Garmin Vivosmart HR gets, but they are the bread-and-butter of smartphone alerts. You can set the device to ping you with a reminder to move if you've been sitting for too long, and you can set a silent alarm to either wake you up in the morning with light vibrations or to remind yourself to do something important during the day.

Listing image by Valentina Palladino