Health and sleep trackers have been around for longer than you’d think, but they've only recently become truly worth our time. Gone are the days of a simple pedometer: Now, if the wristband you’re attached to doesn’t tell you your heart rate, VO2 max, and whether you should’ve had that last Krispy Kreme, it’s positively Stone Age technology. With the rapid development in the sector comes detail, and lots of it. We’ve all signed our lives away to various social media giants and dive bars that have WiFi anyway, so we might as well get some benefits from our personal information floating about in the internet ether. Whoop 4.0 provides them in spades, with some of the most in-depth health analysis on the market. It’s seriously impressive: just be careful what you wish for. So… what actually is Whoop? The whole premise of Whoop as a company is that it brings analysis and personal insight to your everyday life. And lo and behold, the Whoop 4.0 delivers strongly on this, with three major metrics used to help you get and stay healthier for longer. Connected to the Whoop app via your phone’s Bluetooth, the system monitors daily strain, nightly sleep, and post-rest recovery, to give you a score out of 21. To be very clear, this is not a smartwatch. There’s no screen, for starters, and don’t expect to be able to tell the weather or pay for your trendy overpriced cortado. What you will get, however, are intricate readings of your heart, sleep, physical exertion, and recovery, along with useful guidance on how to improve or sustain your status. The latest update also added VO2 max sensor capabilities, something that keeps Whoop up to date with, say, a Garmin. The bespoke nature of Whoop is a major attraction, and consistently works: I hardly questioned its findings, and if I did, I was told why I, for instance, had experienced my worst daily recovery for a month (more on that later). You can also create personal fitness goals, with daily journals keeping you on the straight and narrow. Any exercise is automatically logged, and there's the option to fine-tune upon finishing: tweaking the time, choosing the specific workout you did, and so on. Whoop will also let you know when you can push on or need to sit back. Basically, if you’re ready for someone to check in on your progress every hour of the day, the Whoop is the best choice. There’s little wonder that it’s become a popular thing to own amongst plenty of high-flyers, from business leaders to athletes including Virgil Van Dijk, Beth Mead, and Sha’Carri Richardson. Rory McIlroy wore one during his recent win at golf's Players Championship, revealing that it showed his heart rate drop directly before the decisive putt. Sweet dreams One of Whoop’s biggest assets is undoubtedly its impressive sleep tracking, providing detailed advice on the effect of different sleep patterns and focusing on sleep consistency rather than hours in bed. Advice is provided on the app, but also in longer form emails sent periodically—seemingly when the app has sensed a trend in sleep or fitness. Whoop tracks the four stages of sleep—slow wave sleep (SWS), REM, light, and awake—with each stage bringing something else to your recovery. By monitoring metrics such as the amount you wake up throughout the night, breathing rate and heart rate, Whoop pieces together an overview of your sleep health, and gives you daily recommendations on how to improve your night’s rest. One of the most useful aspects of Whoop’s sleep tech is when trying to improve sleep patterns. As a freelance writer, my sleep behavior is somewhat… erratic. Whoop noticed this, calculating how much sleep I really need based on recent nights and any physical strain from the day. From this, it offers a sleep schedule for bed and wake times, taking into account your wishes of whether you need to “get by” (70% of needed sleep), "perform" (85%), or "peak" (100%). If you set an alarm, you can also programme the band to lightly buzz to help wake you up—much better than the grating phone alarm you’ve been meaning to change for half a year. For a bigger picture, Whoop stores your sleep data to help you identify patterns over the week, month or year and work towards a routine that works for you. It gives you the tools to help yourself: having easy-to-read graphs of my sleep and simple explanations for each aspect has certainly led to improving my habits. And for a health app to recommend I take a nap—and to have to do so professionally—is a modern miracle I never thought I’d see. Are you ready for the truth? We'll be honest, with so many insights available, you do need to prepare yourself for some potentially hard truths from Whoop. If you’ve overindulged one evening, for instance, the Whoop will be sure to let you know, and it's not exactly forgiving. After a rare Friday night out, I fell asleep in the early hours, waking up not much later to be greeted by the Whoop’s daily sleep analysis. If you’ve never seen feedback that you’ve managed to "recover" 3% from the day before, the experience is rather galling. The Whoop doubles down with its pie chart system, detailing said recovery, your physical strain score, sleep performance, and heart rate variability (HRV)—the millisecond variations between heartbeats. Everything was red. Whoop was not happy. I felt like I was in detention. This is why Whoop won’t be for everyone. The metrics it measures are so wide, and its feedback so in-depth, that any variation in your day-to-day health will likely be picked up. Humans naturally gravitate towards bad news, and although Whoop does a good job of softening its language around anything that might not be firing on all cylinders, and offers helpful tips on gently righting oneself, it’s still a tough moment when you see red bars on the app. That being said, this level of analysis will be perfect for a big chunk of us wanting to improve our health. Whoop 4.0 verdict From intricate analysis of the daily strain you put on your body and the almost imperceptible changes in your physiology, to constructive feedback on how to improve your health and the most in-depth sleep tracking we’ve tested, for most people Whoop 4.0 is a good chance to invest in yourself. Thanks to its “always-on” nature, it essentially forces you to prioritize sleep and recovery—you'll find yourself spending more time in bed than ever before. This being said, there are times you need to live your lift a bit and the constant reminders about getting enough sleep can make even just a casual trip to the bar into something that riddles you with guilt. If you have any kind of health anxiety, keep in mind that it might make breaking out of those thoughts all the more challenging. This story originally appeared on British GQ.