Fitness Tracker Review: Fitbit One, Fitbit Flex & Jawbone UP24


Fitness trackers are motivators. While, on the surface, they claim to record data about your activity, the real reason people buy them is to motivate themselves to be more active. None of them are perfectly accurate, and they all have drawbacks. Some have good hardware and mediocre software; some have excellent software and poor hardware. But, if you want this kind of device, there is certainly one that will fit your needs.

I’ve tried three fitness trackers: the Fitbit One, the Fitbit Flex, and the Jawbone Up24. I’ve had the Fitbit One for about a year and a half; I tried the other two recently. Here are my thoughts. (Note that all three of these devices sync to a smartphone by Bluetooth; the Fitbit devices also come with a USB dongle to sync to a computer. Also, each of them uses a proprietary connector to charge; it goes into a USB plug, but it’s yet another cable to worry about.)

Fitbit One

The Fitbit One (, Amazon UK) is a tiny tracker that you can either clip onto your pants or belt, or carry in your pocket. It tracks steps, and a built-in altimeter counts the number of floors you climb. At night, it can also track your sleep, both in time and quality. The latter assessment is based on how restless you are at night.

pnl1_fitbit_one.jpgAs I said, I’ve been using the Fitbit One for about a year and a half. I bought it for two reasons: to motivate me to become more active, and to lose some weight. The Fitbit software takes the data from the tracker and calculates the distance you’ve walked, and the number of calories you’ve burned each day; you can set goals and try and reach them.

I’ve been using this in conjunction with Fitbit’s Aria wi-fi scale (, Amazon UK), which records my weight and syncs to the Fitbit website, where that data integrates with data from the tracker, and displays in the Fitbit iOS app.

The Fitbit One is discreet, and doesn’t get in your way. Since you wear it on a waistband or belt – or even stick it in your pocket – you don’t have to worry about it being visible, which is not the case with the wristband trackers I’ll look at below. However, I lost the first Fitbit One I bought, when traveling; its clip wasn’t as tight as I’d like. The replacement I bought is tighter, and I’ve had it for about 15 months.

The Fitbit One is very accurate at counting steps; it’s in the best location to do so, right around your hips, where you would wear a simpler pedometer. Fitbit’s iOS app lets you watch your steps live, and I’ve tested the One walking on various types of ground and at different speeds, and it always registers steps. As for floors, however, that’s not so precise. It counts a floor if you go up or down ten feet in altitude; your floors may be more or less than that, and I’ve found that the floor data is pretty useless.

I don’t use the Fitbit One to track sleep. It comes with an elastic wristband, into which you slide the device, to wear at night. It’s uncomfortable and annoying. I tried it for a few nights, then gave up.

Overall, the Fitbit One is a good device, as its step count is extremely accurate. Fitbit’s software – both on iOS and its web-based dashboard – is useful, though relatively simple. It doesn’t offer reminders and nudges as the Jawbone UP does; it essentially offers just raw data. While I want more – the inactivity alert the Jawbone can provide would be useful to remind me to get up and move during the day – it’s good enough for now.

Fitbit Flex

The Fitbit Flex (, Amazon UK) is a wrist-worn Fitbit device. Offering the same tracking data – with the exception of floors – this device is quite limited in its ability to convey information. While, with the Fitbit One, you can press a button on the device to cycle through the day’s data, the Fitbit Flex only shows a few LEDs to tell you if you’ve reached your goal.

61YRYwYtSJL._SL1500_.jpgUnlike the Fitbit One, the Flex is very inaccurate. It records around 20% more steps than the One, and during a 15-minute drive to a grocery store, it recorded about 100 steps (tested in both directions). Since it’s worn on the wrist, it cannot be as accurate in counting steps; using Fitbit’s iOS app, which shows a live step count, I can see that it records steps when, for example, I reach my arm to a bookcase to the left of my desk to grab a book and place it on my desk.

If you wish to use it for sleep tracking, however, it is a lot easier than the Fitbit One. The idea of wrist-worn trackers is that you wear them all day, so you don’t need to change the device from your belt to your wrist. However, you do need to tap the device in a certain way to engage sleep tracking (five quick taps just below the LED display), and remember to disengage it the next morning. Last night, I slept, according to the Fitbit iOS app, from 12:29 to 8:28. Yet the software tells me I slept 7h 41mins; the math isn’t that hard, and the difference doesn’t even correspond to my “11 restless minutes.”

The Fitbit Flex comes with two wristbands, in a small and large size. I found the large to be comfortable, and not too tight. However, the clasp that holds it shut is just a piece of plastic that you push through two holes in the wristband; it’s hard to put on, and I can’t see this staying on during, say, a basketball game, or ever when you pull off certain clothes. At the cost of these devices, and given that I’ve already lost a One, I don’t trust this type of clasp.

While it’s comfortable, the Fitbit Flex’s inaccuracy makes it essentially useless. I’ll have more to say about that in my conclusion below.

Jawbone UP24

I was very attracted by the concept of the Jawbone UP24 (, Amazon UK), because, unlike the Fitbit, this device nudges you to be more active. This can be through notifications from its app, and you can set a reminder to warn you when you haven’t been active for a certain number of minutes (the wristband vibrates).

JawboneUp24-582_size_blog_post.jpgI bought the large Jawbone UP24, after measuring my wrist to be 19 cm (the large size is for 18-20 cm wrists). Surprisingly, the Jawbone is tight on my wrist, even though I don’t have fat wrists. I am big-boned, but the size I measured, following Jawbone’s instructions, should be fine with this model. It’s tight enough that the two ends of the device don’t lie flat as they should (as you can see in the photo to the left). The device should also be loose enough to allow air to flow under it, especially if you’re wearing it when active and sweating; this isn’t the case for me.

I took the Jawbone for a walk. I have a treadmill in my house, and walked for a half-hour with the Jawbone on my wrist: it recorded a total of 38 steps, compared to the Fitbit One, which recorded a bit over 2,000 steps.

I looked on the web, and saw this is a common problem with the Jawbone. It measures steps by the movements of your arms, so if your arms aren’t swinging – such as when you walk on a treadmill, or when you’re carrying something – it won’t count that activity. Apparently, it also doesn’t count steps when you walk slowly, such as in a supermarket.

I’ve seen recommendations that you should put it in your pocket when walking on a treadmill, but if you have to do that, it defeats the purpose of using this type of device. So I tried that; the same half-hour on the treadmill, and the same 2,000+ steps with the Fitbit. The Jawbone, in my pocket, recorded 260 steps.

So, an activity tracker that can’t count your activity is not very useful. Add to that the fact that it’s uncomfortable. When I’m typing, the Jawbone gets in the way. The heels of my hands rest on my desk – I touch-type – and the Jawbone is in a position where it touches the desk. I can’t put the jawbone any higher on my wrist, since there’s no extra room; when I try, I can feel that it constricts my wrist a bit. The Fitbit Flex, on the other hand, is as thick as a standard watchband, and doesn’t bother me when I type.

One more thing

I would have liked to try the Fitbit Force, the most recent Fitbit product. This is a wrist-worn device, like the Flex, but which offers more options, and a real display (it can display numbers, not just LEDs, and also shows the time of day). However, this device has been recalled, because of a large number of users who got rashes from its plastic. Also, it has a similar clasp to the Flex, and I’d probably be afraid of losing it.


What’s the point of an activity tracker if it’s not accurate? Of the three I’ve tried, the Fitbit One, because of its location, is clearly the most accurate. If you have set a goal for your activity – most people use the arbitrary round number of 10,000 steps per day – you’ll hit it a lot quicker with, say, the Fitbit Flex than the One. Which means that you won’t be as active as you want.

The software for these devices also counts calories. If you’re trying to diet with a specific calorie restriction, the incorrect step count will also give you a very skewed calorie count. For a difference of +/- 20% in steps, this leads to a similar difference in calorie count. (And I won’t even go into how arbitrary calorie burn numbers are…) For example, I’m wearing both the Fitbit One and Fitbit Flex right now. It’s early in the morning, and I haven’t walked much yet (I work at home). The Flex shows that I’ve taken 582 steps; the One has counted 367 steps. That’s a huge difference. (A few minutes later, I haven’t taken any steps, and the Flex counted another six of them; because of my arm movements.)

It’s not just the inaccuracy of some of these devices that bothers me; it’s the fact that they are even on the market. If a device that claims to count your steps is not accurate, then it’s not performing it’s most basic task correctly. I understand that this is a difficult technology to perfect. The Fitbit One, worn in the correct location, is the most accurate; as for others, perhaps you simply can’t make an accurate wrist-worn tracker. Many people will buy these because they are very visible gadgets; but they’re little more than fashion accessories. If the basic information they give you is flawed, then there’s not much point.

Note that I could use my iPhone 5s to count steps, as it has a special chip that counts and records such information from its accelerometer. But my phone isn’t always in my pocket when I’m walking – when I walk on my treadmill, I put it on a window ledge – so it wouldn’t count everything. And when I walk around the house during the day, I often leave it on my desk.

As I said earlier, these devices are motivators; they can help you be more active. If you simply want an idea of your activity relative to other days, pretty much any device will give you that. If you want more accuracy, I’d recommend the Fitbit One, which counts your actual steps.

(I’d be interested in comments from readers who have any of these devices, or any others, as to their accuracy.)