Whether you workout daily or have been trying to kickstart the habit, a fitness tracker is a great way to enhance your exercise routine. While we’ve tested plenty of fitness trackers, over the last few months we’ve been trying the Whoop Strap 4.0 and think it’s a standout option for people who take their health and workouts seriously.

We’ve previously tested the Whoop Strap 3.0 and loved how it felt like an in-depth personal trainer on your wrist. Now, Whoop has released the new and improved Whoop Strap 4.0 which is smaller, smarter and jam-packed with new features like skin temperature readings and a haptic alert.

After spending months with it tracking our workouts, sleep and recovery, here’s what we think of the Whoop Strap 4.0.

An in-depth fitness tracker for the serious athlete

The Whoop Strap 4.0 gives you unrivaled, in-depth data and analysis to your health. It improves upon the 3.0 and is a fantastic fitness tracker for people who want to optimize their exercise and recovery routines.

The who, what and how

Who this is for: The Whoop Strap 4.0 is for people who want to optimize their workouts and recovery. If you’re just looking for a strap to count calories and steps, a tracker like the Fitbit Inspire 2 will do the job. However, if you’re an athlete or a fitness fanatic who craves in-depth data, the Whoop Strap 4.0 is for you.

What you need to know: Whoop Strap 4.0 is smaller and sleeker than its previous iteration with a few added features like skin temperature and blood oxygen readings, as well as a haptic notification alarm function. The brand also released Whoop Body, a line of clothing that can hold your Whoop tracker so it doesn’t always have to be on your wrist. However, like the Whoop Strap 3.0, this fitness tracker requires a membership. You can join for $30 per month with a 6-month membership, or commit to a longer membership and pay as low as $18 per month upfront, totalling $324.

How it compares: The Whoop Strap 4.0 is definitely a worthwhile upgrade from the 3.0. And if you already have a Whoop membership you can get the upgraded strap for free. Compared to other fitness trackers and smart watches, it offers a deeper dive into your health that’s super useful in tailoring how you approach your exercise day by day, but the Whoop Strap 4.0 is purely for fitness. The other big difference, again, is that the Whoop Strap is a monthly membership compared to other trackers that you buy outright. Amazon’s Halo and Halo View offer a similar formula, but rather than just providing more data, they toss in recipes and workout classes too.

The Whoop Strap 4.0 improves on its predecessor’s design with a sensor that’s 33% smaller. When we tested the 3.0, we didn’t really think it felt bulky on our wrist, but when we put on the 4.0 we immediately felt the difference. It’s much smaller and feels noticeably more comfortable.

Kai Burkhardt/CNN

Whoop has also reworked its strap and clasp system, which is what holds the sensor on your wrist. The material of the strap feels much better than the old version with a smoother, softer design. Instead of unhooking both sides of the clasp from the sensor like you would on the 3.0, the 4.0’s clasp easily slides off so you can spend less time taking your old strap off.

On top of these upgrades to the band itself, Whoop has also created an all new, waterproof battery pack. This was a massive game changer for us because now if you accidentally forget to take the battery off your strap while you’re washing your hands or doing the dishes, you won’t need to worry about it breaking. The battery pack still adds some bulk to your wrist since it slides onto the strap to charge, but even with it attached, the Whoop 4.0 doesn’t feel bulky. In fact, it’s about the size of a standard smart watch.

Thankfully, Whoop has kept the same battery life for both the sensor and the detachable battery, meaning it takes about two hours to charge the pack and an hour and a half for the pack to charge the strap. That full charge will give you about five days of juice, so you don’t have to worry about charging it all the time.

Whoop’s core of Strain, Sleep and Recovery is still stellar

While the physical improvements to the 4.0 are great, Whoop made upgrades to the tracking and app that makes the new strap even more in-depth and easier to use. Whoop 4.0 features an updated sensor configuration that provides more accurate readings, and during our testing, we didn’t see any drops in measurement accuracy from our time with the Whoop 3.0. The 4.0 tracked all our workouts, sleep and recovery extremely well, even during the hardest sessions on the Peloton. The Whoop 4.0 can also track skin temperature and blood oxygen levels, two measurements absent from the 3.0. This brings it in-line with other trackers from Fitbit, Samsung and Apple.

These added health measurements add to the already abundant amount of data that Whoop can give you, but luckily they’ve introduced another element into the app to help you easily keep track of all these data points. A new Health Monitor section opens up a little box on your phone that tells you when your readings — which include skin temperature, blood oxygen level, resting heart rate, respiratory rate and heart rate variability — are in their normal ranges. If they aren’t, it will give you a list of potential causes for the change and if you’re worried about it — or just heading to your annual checkup — you can print and share an in-depth health report right with your doctor.

Kai Burkhardt/CNN

This Health Monitor is also available for members that still use the 3.0 (all you need to do is update the app if you haven’t already), however skin temperature and blood oxygen levels won’t appear.

Besides these added features, the day-to-day experience of using a Whoop Strap 4.0 was very similar to the 3.0. We woke up each morning, answered a personalized questionnaire about the previous day (we liked to track stress, hydration and caffeine and alcohol consumption), checked out our recovery score and tailored the day based on how recovered our body was.

We still love Whoop’s strain, sleep and recovery method — which you can read about in detail in our Whoop Strap 3.0 review — and think it’s an extremely useful tool to help prioritize your health. Using the Whoop Strap has made us much more wary of our exercise routine and the amount of sleep we get each night. In fact, it wasn’t until using the Whoop Strap that we finally realized that a good night’s sleep actually requires more than 6 hours in bed.

The other big improvement in the 4.0 is its haptic alert, which you can use as an alarm in the morning. In the Whoop app, you can schedule the alarm to go off when you’ve reached a sleep goal so you can be sure you’re fully rested. If you’re getting to bed late and your sleep goal isn’t until 30 minutes after you have to log on to work, there’s a feature where you can set your latest wake time so you don’t oversleep.

Kai Burkhardt/CNN

We used the haptic alarm quite a bit during our testing and loved the idea of optimizing our wake times with our sleep goals. However, more often than not we didn’t get to bed early enough so we were waking up at our latest wake times anyway. Another plus of this haptic alarm is that if you sleep with a partner, it isn’t a loud alarm like the one on your phone, so it’s easier for your significant other to stay asleep. The alert itself isn’t customizable, which we would have liked to see, however, we think it’s strong enough for most people but it won’t scare you awake.

The haptic alarm is useful, but we’re eager to see where Whoop takes this feature in the future. We’d love to be able to personalize this haptic notification even more, so we could remind ourselves to drink water, get ready for bed, stand every hour or even use it as a timer for workouts.

Whoop Body takes tracking off your wrist

Alongside the Whoop Strap 4.0, the brand released a clothing line called Whoop Body. The line includes clothes for both men and women, including tops, bottoms and even intimates, all with little pockets that can hold the Whoop sensor so it doesn’t always have to be on your wrist. We tried out a couple pairs of the Any-Wear Athletic Boxers, which holds the sensor on the inside of the waistband on the left side. The placement of the sensor in all pieces of Whoop Body was specifically chosen to maintain the tracker’s accuracy, so unfortunately you’re stuck with the one position.

ANY-WEAR BOXER

Wearing the boxers was a great experience, as it frees up your wrist giving you the ability to wear a watch or just take a break from having something on your arm 24/7. Slipping the sensor into the boxers was a breeze and we didn’t see any difference in tracking performance between the boxers and the normal strap.

The boxers themselves felt really nice, with an athletic, soft material. The waistband was a little thick and they had a tendency to ride up, but they were in no way the most uncomfortable pair of underwear we’ve worn. In fact, we were surprised by how little we noticed the sensor as we went about our day, even when we were exercising or laying on our side.

Whoop Body is a great option if you want all the benefits of wearing a Whoop but don’t want to deal with a strap all the time. However, with clothing options starting at $54 it would be expensive to use Whoop Body as your primary tracking apparatus, but it’s a convenient way to mix things up.

The one big caveat to consider is the pricing structure of Whoop. You can sign up for a membership for $30 per month with a six-month membership, or save in the long term with a 12- or 18-month membership at an upfront price of $288 and $324 respectively. The membership comes with the physical strap and access to the app, and as Whoop continues to improve — whether that’s adding more features or even releasing updated hardware — it will most likely be included in the membership as well. That means you won’t have to buy the latest version of your tracker every year like other competitors, and as long as you’re a Whoop member you can take advantage of the constant improvements the brand makes to its product.

Kai Burkhardt/CNN

The Whoop Strap 4.0 is a high-quality, in-depth fitness tracker perfect for athletes looking for insights about their health. The improvements from the 3.0 don’t distract from what makes Whoop special, which is helping you take an informed, data-driven approach to your exercise and fitness.

The physical updates such as its smaller size and waterproof battery pack make using the Whoop on a daily basis painless. Additionally, we love how the new software features and tracking give you more tools to optimize your health.

With its physical improvements, feature-filled app and the addition of Whoop Body, the Whoop Strap 4.0 has made digesting fitness data easier than ever before. If you have serious fitness goals and want to exercise, sleep and recover as best as you can without an actual personal trainer, the monthly price of Whoop is well worth it.