Fitbit Flex Wireless Activity + Sleep Wristband

A slim and stylish device that stays with you at all times, the Fitbit Flex keeps track of steps taken, distance traveled, calories burned, and your sleep cycle to help you reach your personal fitness goals.

$ 99.95

Customer Reviews

2,739 of 2,850 people found the following review helpful
4.0 out of 5 stars
Jawbone UP vs Fitbit Flex — Fight!, May 17, 2013
RST (USA) – See all my reviews

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Several asked my opinion of the Flex after I had compared UP to ONE last fall. I’m more pleased with Flex than expected. This review will be specifically for those comparing the Jawbone UP to the Fitbit Flex. For those interested in my review of the One and Jawbone UP it is located here: UP by Jawbone – Large Wristband – Retail Packaging – Onyx:

UPDATE: I uploaded several head-to-head app screenshots.

UPDATE: I’ve found that I am storing quite a bit of water in the Flex band pouch where the module goes. Even though they say it’s shower safe, I’m pretty sure some funky stuff is going to be growing in there in a matter of time… But the band is replaceable!


My journey with personal monitoring devices/pedometers started a LONG time ago: Before Fitbit even existed, with a device called the SportBrain. It was a traditional belt clip style so old that it plugged into a base that used a dial in phone modem to upload the usage data to a server. It was old. But my interest in devices that can help monitor and tell me about my activity started then, and we seem to be now in a golden age of personal data monitoring devices. Fitbit Flex, Jawbone UP, all of the Fitbit clip devices and so many more…

Hardware itself

The biggest drawbacks I found on the Jawbone UP were that it had no visual feedback about your daily achievement toward your goal and the fact that it had no visual battery indicator. It wasn’t a problem for me personally, but for those who are hardcore driven on a daily basis to compare and achieve this could be a drawback for you. The next drawback about the Jawbone UP is that it does not wirelessly sync. You have to plug it into the headset jack of your phone to sync. If you are someone who wants data and feedback all day long, this would be a drawback.

The Fitbit Flex does have visual feedback in the form of small white lights: They blink as you’re charging, they have a special blink if you put it into sleep mode and provide 95% more feedback than Jawbone up. Jawbone UP does have status lights in it and they are used, but they could do a lot more with the lights they already have if they chose to.

If you can throw a snap bracelet on, you can easily put on the UP. I did find myself fumbling a bit with the clip mechanism of the Flex like I do when I have to button my own shirt cuffs. After it was clipped though, it feels secure and I am not one to put on and remove devices like this. I want to set it and forget it.

Fit & Feel

The Fitbit Flex feels very comfortable on the wrist. The pictures don’t do it justice. For me personally this is the one defining factor that really makes the Flex shine for me compared to the Jawbone UP. It feels super light weight, doesn’t grab, and doesn’t look nearly as big/thick as the pictures make it look.

The UP uses tension to stay on, while the Flex uses a clasp. The UP may have a better sense of solid attachment that wouldn’t come off no matter how hard you fling your arm, but the inverse of that is the Flex: It doesn’t have to monkey-grip your arm to be there and stay. You can have it fit a bit more loosely than UP and be comfortable.

When typing on at a keyboard, I prefer the feel of the Flex. The rubber is flat and thin so it adds very little against the edge of a keyboard. The UP doesn’t have the big square bump on the top, but it does have a bracelet shape/size all the way around, so it can prove a bit more of an annoyance up against a keyboard.

The Flex does have replaceable bracelets and colors, which means the device is more convertible and flexible going forward. That being said, it is less visually appealing to me compared to the UP. The UP can be a part of jewelry and most people would never notice. The Flex does have a strange-ish future nerd look to it. I don’t mind that, but some may.

I wear both in the shower with no issues. I’ve done a lot of swimming pool roughhousing with the UP with no issues, but haven’t tried with the FLEX. A commenter tells me that it is swimming approved, though the data provided might not be that useful.

Battery Life & Charging

Both the Flex and the UP charge in very similar almost identical USB adapters. They’re meant to be charged on a computer and in my experience shouldn’t be charged off of a phone USB wall charger. They both charged in similar amounts of time, and the Flex did last about 4 days on a charge. The UP can last as much as 10 days on a new battery, but I found that it has declined some since November. On this case, I say that both do about what they suggest. The UP fits snugly in the charger, while the Flex doesn’t feel nearly as secure in…

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3,679 of 3,842 people found the following review helpful
3.0 out of 5 stars
Well, if the the Flex WINS the ‘Fight’ over the Up, you’d better read this…, April 16, 2013
D. Graves “Fine Books and More” (Portsmouth, New Hampshire) – See all my reviews

The Flex is pretty good – IF you understand its limitations. And it has a lot of them. This is a 1.0 version, the first wrist-based tracker Fitbit has produced. Since the positive reviewer claims the Flex clearly wins its ‘fight’ over the Jawbone Up, I strongly suggest you wait for the technology to be refined by Fitbit (and others) before spending 0 or more on this.

I also suggest that you tune out the 5-star “this is AWESOME!” reviewers. I’ve had the Flex for 6 months now (acquired at CES 2013, long before retail availability) and initially I too was impressed by the technology. However, with long-term use, I think its inaccuracies make it nothing more than a pedometer with sleep analysis added in (and the usefulness of the latter is dubious as well). The IDEA of it all is excellent: to track your activities and see your progress over time via the great software that Fitbit has developed. However, all of this is predicated on the device accurately tracking your movements. If it fails in that aspect – and unfortunately it does, to a moderate degree – then all of the data and impressive charts and graphs are rather useless. The “awesome!” reviewers don’t realize this (yet) and just assume what they’re seeing is real; it isn’t.

The underlying technological problem, as I see it, is in the placement of the tracker. Up until now, Fitbit trackers were to be placed on the torso. Now, it must be placed on the wrist (yes, the tracker itself can be taken out of the wristband and put into your pocket but all of Fitbit’s calibrations and algorithms are designed for that wrist placement and you are making the problem worse by not having it on your wrist). So, if your wrist movement is ANYTHING other than the usual movement of either running or walking, your step count/mileage is going to be off – often way, way off.

Fitbit markets the Flex as an “activity monitor”, implying that it is capable of keeping stats on your physical activities. Well, because of the wrist location issue and the basic design structure of using two stride lengths for all calculations (your walking and running stride lengths), pretty much any activity that is NOT walking or running cannot be accurately monitored: the accelerometer senses whether you are walking or running and multiplies the appropriate stride length by the number of steps sensed (and arrives at a mileage distance). Any activity outside of that limited ability of the Flex, your stats are innacurate. This includes stair-climbing, hiking, tennis, golf, biking, working out, and pretty much every other “activity” that is not walking or running. The Flex is not really an “activity monitor”; it’s an expensive pedometer (albeit one with “sleep analysis”, which is actually only a record of how much wrist movement you had during the night: i.e., 2 hours of no movement = deep sleep, an hour of sporadic movement = restless sleep).

There are, however, aspects of the Flex that are quite good: it does accurately keep track of your walking and running, it does keep track of your sleeping patterns, and it also wakes you with a silent vibration on your wrist at the time you set to get up in the morning. And once out of bed and into the shower, there’s no need to take the Flex off: it’s almost completely waterproof (pressurized water being the exception). But the best, perhaps life-enhancing aspect of the Flex is its ability to keep you focused on your exercise goals (which is the main reason why, overall, I like the device and its software – to a point): if you DO consider it only a pedometer with cool software, which is what I consider it to be, you will not be disappointed (though the price may not seem worth it to others).

First, there’s the ‘onboard’ function to keep you aware of your progress towards your daily goals (total distance traveled, number of steps taken, or calories burned): each light on the row of 5 small LED lights on the band represents 20% of your goal and a quick glance and a tap on the band will tell you how you’re doing. Secondly, for the actual stats of your progress (or reviewing your daily, weekly or longer stats), you can view them in real time on your phone via the Fitbit App for iPhone and Android, or on your tablet or PC/Mac with the Fitbit ‘Dashboard’. This is where you set your daily and longer-term goals, view not only your stats but see them represented in charts and graphs, and log other information such as weight, weight changes, and food consumed. You can go further, but personally I would feel a bit silly setting goals where I would receive ‘badges’ for reaching them. But that’s just me. Overall though, the software is very good and keeps you aware – along with the band’s LEDs – of whether or not you are staying on track of exercise goals. But, again, just keep in mind that the wrist placement of the device gives the Flex an inherent flaw as to the accuracy of all this data – UNLESS you are using it…

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1,109 of 1,210 people found the following review helpful
4.0 out of 5 stars
Fitbit gets it right with the Flex, but there are some minor quirks, May 3, 2013
My wife and I purchased our Flex bands early at Best Buy like so many others have already done. This is my first Fitbit product and activity tracker, so please keep that in mind. First off, the product’s presentation is stellar and will no doubt be an attractive offer to people checking it out in the store. It comes with two sets of bands (large and small), a USB charging dongle, a USB syncing nub, and the activity tracker itself. One knock I have is the lack of a physical manual that comes with the product. There is literally one piece of tiny paper that just has the setup URL. It would have been nice to have at least a 5-6 page quick guide to how this thing works. Setup is a breeze, just go to the URL listed on the paper, download the software, and sync your tracker with the USB syncing device. It asks you to “double tap” the device to sync, I felt like a neanderthal trying to find a button to press. All you need to do is tap the top with your index finger like you would a mouse button.

Getting the tracker in and out of the different bands is easy and it becomes obvious when you put it in the wrong way. Actually putting the band on your wrist is a different story. It’s comfortable when you have it on, but it’s difficult to push the clasp together to hold it on. It becomes especially difficult with the smaller band because you have less room to work with. See, you want to have the band on snugly so it doesn’t move around, but in order to do that you can’t have a finger inside of the loop to help push the two ends together. It doesn’t feel like it wants to come off when you do have it on though. Also, I spend a lot of time at my keyboard and it’s very comfortable to type with it on. (this surprised me)

My wife and I both have Galaxy S3s and the syncing is pretty seamless. It appears that the syncing frequency between devices is at 15 minute intervals. It takes a minute to manually sync devices, but I don’t feel like that’s necessary unless you’re in desperate need of motivation/feedback. My wife and I went on a walk shortly after we got our Flexes and the devices appears to be accurate, but I haven’t really scientifically tested that claim. I read somewhere that these wrist devices sometimes mistake arm movement for steps, but that is not the case here. It’s really a bummer that it doesn’t have a built in altimeter like the Ultra and I imagine that the 2nd generation Flex will have that built in. As for the activity lights, I thought they would be always on, but instead you have to double tap the device for them to show up. That’s not a bad thing, but it’s something to note.

The sleep tracker/silent alarm function was a huge selling point for me with this device. I’m a little disappointed that the sleep tracking/alarm isn’t as robust as the Jawbone Up’s. See, there is no detailed analysis of the quality of your sleep, but instead it only tells you when you slept and when you got up in the night. I realize that sleep tracking (deep sleep vs. light sleep) is pseudoscience, but it would be a nice data point. The alarm will just go off when you set it, so don’t expect it to wake you up when you’re more “rested” like some phone apps or the UP. (again, more pseudoscience) The silent alarm is really not very silent at all. If you have your wristband up against anything besides your wrist it will vibrate the hell out of it. This isn’t a knock against the product, but just be warned this device will wake you right up! The vibrating motor feels just as powerful as any smartphone. Also, there is no automated nap feature like the UP, but the alarm is easy enough to set for your own nap intervals.

EDIT: So it appears that there is a device setting on the Fitbit website that allows you to set the sleep tracking to “Sensitive”. This might be more of what I’m looking for as opposed to the binary data of the default setting. (i.e. awake or asleep)

The Fitbit software is pretty standard at this point and should be familiar to most of you. The only difference is the alarm feature is baked right in. It’s not the most complete set of features, but it gets the job done and is extensive enough for mobile devices.


– Comfortable (even at a desk!)
– Stylish
– Activity Lights for Progress
– Accurate (this hasn’t been fully tested, but will say it is for now)
– Adjustable Size Wristband
– Silent Alarm/Sleep Tracking

– No altimeter
– Sleep tracking isn’t as robust as the UP
– Difficult to put on


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