Review – FitBit Flex

The Fitbit Flex and all of the accessories

Everyone’s heard of them – activity-trackers.  They are devices that you wear on your wrist or in your pocket or another place on your person and which monitor and track your physical activities – whether it is general movement, steps, stairs, sleep, etc.  If you want to keep a bit of an eye on what you are doing, need to lose weight or get healthier then you might want to consider an activity tracker.

fitbitAnd the Fitbit Flex is one of the most popular of the whole range of activity-trackers, and pretty good for step- and sleep-tracking.  

I say ‘pretty good’ because it’s not perfect; nor should you expect any of these devices to be.  If you’re looking for high accuracy, precise step and distance tracking and exact calories burned as well as exacting standards in sleep monitoring then you won’t find it in the Flex nor will you with any device that is in it’s price range and small size.  In fact for that you’d probably need a whole host of expensive medical equipment.
But for slightly more precise distance measurements but a higher price you might want to consider instead (or in addition to the Fitbit) a GPS fitness watch, though they are not exactly made for 24/7 use but geared more toward individual fitness and sporting activities.
The Fitbit Flex in the large bandWhat you will find in the Fitbit Flex is a device that will use motion tracking sensors to give you a fairly good idea of how many steps you have taken/distance traveled, will give you a general idea of calculated calories burned and log your steps, as well as give you some stats on general sleep activities – for a relatively cheap price.  

A quick note – the Fitbit does not have a heart rate monitor and as of right now there are few of the cheaper activity trackers that do – like the Garmin Vivofit.

Indeed the Flex and other similar devices are amazing devices, packing incredible tech and software (though a good amount of the processing of your data gets done externally; through the company’s servers and website and the apps that connect to it) into a tiny package that would be unimaginable a few short decades ago.  
So whether you are trying to lose weight, get healthier, or just monitor your activity and sleep you are going to find the Flex a good way to keep track of things – unobtrusively and without need to do much of anything but put the device on your wrist and tap the face once in awhile at sleep time, and of course charge it when it needs to be charged – and it does hold a charge for quite some time.
The first thing you want to do is to go to the “Get Started” link on the Fitbit website, download the software for your computer/Flex, and run the software – which will walk you through the rest of the process for the most part.  Once the software is installed the driver for the USB dongle is installed also and you’ll be able to plug it in.  
The USB dongle

The USB dongle

One note here; if you use a USB hub (to add more USB ports to your computer) the dongle may or may not work in it – and you might have to plug the dongle directly into the computer (or use a straight USB extension cable).  On my computer, even with a nice high-powered USB hub it didn’t seem to work well and had to be directly plugged into a free USB port.

Once it is connected and synced the dongle will automatically transfer your step and sleep data from your Flex whenever you are anywhere near the computer.  In Windows you can also use the Fitbit icon in your computer’s Notification area on the Taskbar to manually sync your Flex too, and you’ll find some options and other things there too.
App DashboardAdditional note; I don’t have a mobile device which is compatible with the ability to wirelessly transfer and connect directly to the Flex, but it is a similar procedure to pair your Flex to the app if you have a compatible mobile device.  
I do have the Fitbit app for both my Android device as well as the one for my Apple IOS device, but only certain devices will connect directly to the Fitbit Flex and transfer data.  The devices which do will give you some additional things that you can do like the ability to monitor your steps in real-time.  But for those devices that do not connect directly to it your Flex you can still see how many steps you have taken and sleep activity (synced the last time your Flex was near your computer), and do everything you can on the Fitbit website including manually adding activities, sending messages to friends and seeing how you are comparing to them, etc.  So don’t forget to get that app!
Screenshot from Fitbit.comYou probably want to tweak some things on the website under the Settings (which you can find under the gear icon on the far right) – like under your Personal Info you can enter your precisely measured stride distance when walking and running and inputting these into your settings on the site.  An important note here – the company uses the word ‘stride’ and ‘step’ interchangeably, where other sites and definitions might consider a ‘stride‘ to be both the left and right step combined.
The default stride distances might even be fine for you as they are set for the average stride, but it’s not hard to measure out some distance outside or even in your house, and then count your steps and divide the distance by the number of steps to get your stride. Here’s a bit more about it on the Fitbit help section.
You can also enter other info; age, sex, height, and some preferences.
Pretty much all of the info you enter is initially all private on your public and friend-viewable profile so you don’t need to worry too much about things you don’t want others to see (at least as much as anything is private on the Internet) , this also goes for your displayed activities too. screenshot 2You can change the various levels of privacy on your profile depending on what you want to display publicly, to friends, or only for yourself.  A few years ago there was quite a hubbub about people’s, er, uhm, certain private activities showing up on Google so the Fitbit people set the defaults for all activities and personal info to be private, which is good.  And you can change, in fair detail, the privacy level pretty much all of your stats and info.
Also under your profile and settings you can set up to share your activities on other sites like Facebook and Twitter or even post to your WordPress blog.  You can also see what other apps are connected to Fitbit, like Endomondo, MyFitnessPal, SparkPeople and many others.
Silent alarms can be set up too, believe me these work well and will even non-invasively wake you from a sound sleep.  It’s a great feature and is similar to the ‘alarm’ that lets you know that you have achieved your step goal for the day.  You can set a single alarm or a daily alarm, and up to eight of them and the alarm repeats every nine minutes if you do not acknowledge it.
Under the Device setting you can set what your daily goals want to be, whether it’s steps, distance, calories, or active minutes.  Sometimes active minutes can be confusing to people, the Flex counts consistent active times as active minutes.  You can also set which hand you are wearing it on as well as sleep sensitivity.
Under Notifications you can change how you want to be notified of various things, whether they are low battery conditions, messages, challenges, etc and can be sent to an e-mail address and/or the Fitbit app.
These settings can also be changed on the app, whether it is synced o the Flex or not.
The Flex normally comes with the device itself, a black large and small band, a usb charger, and a usb dongle.  All of which you can buy separately also, if you need extras.


I have small wrists (despite using lots of wrist-strength building exercise equipment!) and the small band just barely fit my wrist when extended fully, it’s maybe slightly tight but wearable.

Both band sizes.

Both band sizes.

The larger band fit me with the clasp around the middle of the little slots it fits into, so there was a lot of leeway for those with larger wrists as well as those with slightly smaller wrists.

I think after a bit you will discover the most comfortable tightness or looseness that you want to adjust it to.  I like it tight enough to stay in place and not slip down over the hinging part of my wrist.  Too loose and it slides down and impedes movement of the wrist, too tight and you’ll see it start to leave marks on your wrist as you do your day-to-day activities.

Empty band (large size).

Empty band (large size).

These bands have a plasticy, almost rubbery and soft consistency, and are very flexible but also very durable.  The Flex itself is waterproof up to about thirty feet and the band is too, of course, though you may find some moisture inside around the Flex where it sits inside the band.  It’s good to dry this out once in a while, both for hygenic purposes as well as keeping the small metal charging contacts on the Flex from getting any gunk on them.

The clasp.

The clasp.

The clasp itself is made of a piece of plastic inserted into the band, with a pair of long projections that slip into the slots in the band.  They’ll ‘click’ into place when they are inserted properly, if they don’t drop down when you insert them then you haven’t pushed or snapped them in far enough.

An issue with the Fitbit Flex that people have occasional problems with is the wrist strap clasp inadvertently opening. The Flex message boards are full of people who have lost their Flex, sometimes finding it again and then losing if all over again, multiple times even.  Fitbit sometimes will replace a lost device, which is nice of them – but this is an issue that really needs to be addressed.  I think Fitbit is an excellent company, and has done a great job with these devices both in the hardware aspect as well as the amazing analysis software that is used, and they seem to have great customer service.  But the clasp problem should be somehow resolved.

There is a Fitbit help page for tips on finding your lost Fitbit Flex and there are even some IOS (like this one – there are more) and Android apps (like this one – there are more) that allow the device go search for the Bluetooth signal from the Flex, allowing you to narrow down where you lost it – though you must be quite close, depending.   Unfortunately only certain devices support Bluetooth 4.0 so not all will work for this.  If you can’t sync with your mobile device then you can’t use one of these apps to search for it either.

I’ve experienced the clasp disconnect issue myself.  I had opened up my main desktop computer and was dusting it inside, and as I was putting the panels back on I noticed that the Flex was gone from my wrist.  After looking around for it and not finding it, I decided to open up the computer again and sure enough it had slipped off while I had my arm inside the computer.

I also had it fall off one other time – I suspect this was partly my fault from not properly snapping the clasp together.  If you don’t hear if click then it’s not secured properly.  And if your clasp is damaged, worn or old you might want to try a new one or just get a new band.

Of course, this is only certain people.  Plenty of others never have any problem with the clasp opening or losing their’s.

There are some things you can do to secure the Flex better.

Some people carry the device itself (minus the wristband) in their pocket or something, but the Flex is designed to be worn on the wrist and this may affect it’s function (other Fitbit devices are designed to be kept in your pocket, hung from your pocket or belt, etc).

You can also buy small plastic bands that slip over the clasp to hold it in place.  There are wide ones as well as thin ones, or you can even go to your local hardware store and buy a thin ring of rubber/plastic that is actually an o-ring gasket.

I tried some of the thin transparent rings that came in a set of four.  They worked fine and held the clasp just fine but their thinness allowed them to ‘roll’ up and down the band slightly, so that it was a good thing that there were four of them as at least a couple stayed in place.  But loosening the band some seemed to alleviate this problem a lot.

The wider ones obviously would not have this ‘rolling’ problem but they are also larger and add more obtrusive perhaps.  They do come in lots of colors and various thicknesses so you can get a thinner one if needed.   I’ve read a number of posts on the Flex forums and they seem to work fine for people.  I haven’t tried the wider ones so maybe someone who has one can post a comment and let us know how they work.

I’ve also read that some of replacement, third-party bands are not as durable nor as secure or well-made as the original ones.  But some are and their slightly differing designs may mean they will work better than the original ones for you. You can also get some different colors and designs than the original ones, including camo, etc.

Or you can buy many colors of bands directly from Fitbit website itself.


I have one of the cheaper third party knock-offs which has a very slightly different slot for the clasp, and the clasp is a bit more curved.  It has yet to fall off but when I do anything where the band may be tugged or pulled, or when I am away from home – I use my own discovery for a secure method of holding the band on.

You know those gel/soft bands or “awareness bracelets that charities give you to publicize their charity, or that have sayings and promos/ads for various things?  

Yellow gel band over the Fitbit Flex bandBlue gel band over the Fitbit Flex band

Well, I found that for my wrist the gel bands fit perfectly over the Fitbit band, loose enough so that the band still has plenty of space and slack on my wrist but the band is completely covered, securing the clasp from opening as well as protecting the entire Flex – in case of rough conditions.  And they come in various and many colors.

You can show your support for the charity by wearing it normally and displaying the lettering for whatever the band is made to publicize, or twist it around to the blank side for a solid color.

You can still tap the face of the Flex but unless you are in a somewhat low-light condition you may not see the light indicators, so in bright sunlight you may need to move to shadow to see the lights through the band.  A bit of a drawback but I think it’s worth it, and if you need to you can slip the gel band slightly to the side to see the lights.  I think it’s possible to get transparent ones but I have yet to find them.

Sites like also sell a number of bands and holders for the Flex.

The Fitbit Flex module itself (all display lights illuminated).

The Fitbit Flex module itself (all display lights illuminated).

The Flex itself is a tiny black rounded rectangular piece of plastic.  It’s small 
so don’t lose it!  But most of the time it will either be in one of the bands or occasionally in the charger so there’s little worry of actually losing the device itself.  

It holds a charge for many days, five according to the company – which is about what I get.  The battery life may be decreased by using the vibration alarms a lot.  If you have it set up correctly in the Notifications on the website it can e-mail you and/or send you a message on the device you have the app installed on when the battery gets low.  I even set up a text message alert in my e-mail for when it gets low.
Charging takes a few hours at least (the company says about three but it seems to be less for me), and shows your charge level on the face of the Flex as it fills the charge.  
To manually check the battery charge you can go to the Fitbit site and click the gears/settings icon, which drops down a menu and which displays the battery power that you have left.  The Fitbit app also shows your battery level.   But unfortunately there is no way to check battery charge on the display of the Flex itself.
The actual Flex slides into one of the bands, and of course you have to put it in a certain orientation, which you will get used to doing.  While holding the band with the slotted part upward and looking at the slot for it in the bad – the grey arrow on the Fitbit itself faces upward as you slide it in.
There’s not much in the way of display info on the Flex itself.  It consists of five small LED’s across the top.
Once the Flex is in the band you can tap the top of the band to see how much of a percentage of your daily steps you have done or to switch to sleep mode, or out of sleep mode.
WalkingThe default number of steps is 10,000, as recommended for the average person per day.  You can change this to whatever you want to in the website or app, on the website you would go to the tile on the Dashboard display and hold you mouse over the bottom of the tile under you see the gear icon drop down, at which point you can click it and change it.
In fact it works the same way for any of your goals, pick the appropriate tile whether it is steps, distance, calories, active minutes, etc and click the gear icon to set that goal.
As you go through the day you can check your progress by tapping the top of the band three times.  
Each of the five little LED’s represents 20% of the number of primary goal (usually steps) that  you have specified for yourself.  Solid lights mean you have accomplished that 20 percent, flashing means you are working on that level.
A weird thing I wanted to mention here…well, I guess it’s not so weird taking into mind how the Flex touch control works but it’s something to keep in mind.  A few times when I have been hammering a nail the Flex thought that I was pressing the controls, and I had to bring it out of sleep mode and take it off temporarily.  And a few times certain shopping carts even did the same thing.  Not all shopping carts, just certain ones that has bad tires. The vibration again I suppose.

Tap the top of the Flex twice to see how your progress is going, each light is 20% of the goal that you set in your dashboard.  Usually this is steps but it can be calories, miles, etc instead if you wish.  Set this in your Dashboard under the appropriate tile.  A blinking segment is the part of the goal you are working on, solid ones show a completed goal percentage.  Once you reach your goal it will soundlessly vibrate on your wrist and flash the lights in a pattern.

If you haven’t been near the dongle or a compatible Android or IOS device that can sync the data from the Flex it can store around seven days worth of detailed info and about thirty days of daily activities.

sleepTo start tracking your sleep tap the flex real quickly for a few seconds.  This can sometimes be tricky to learn – tap it twice to get your goal results, tap it quickly for two or three seconds to enter and exit sleep mode.  Doing any other tapping while in sleep mode just shows two blinking lights instead of progress until you switch it back out of sleep mode.  You can also enter and exit sleep mode on the app.

Midnight is when the Flex resets and starts tracking for a new day, but this also can be changed if you need it to be.  Perhaps you work late and want your next day’s tracking to start after your next sleep period.

The accuracy is fine, it’s not going to be on the high end of accuracy unless you use something with a GPS of course, but it does well for the small size and price range.  And it is going to give you a general idea of what you have done during the day.  There’s really nothing else you need to do but keep walking, moving, and exercising.

Some people who use the Fitbit find it counting steps for things like using a computer, driving a car (there’s an Android app that can help you with that), or other things that shouldn’t count as steps.  It’s the nature and limitation of the movement sensors and software so sometimes you may find some inaccuracy creeping in.  Make sure you have the Flex on the wrist that you selected in the settings – dominant or non-dominant.

To do one informal test of it’s accuracy for non-step related activity I manually synced the Fitbit, checked step number, ran three miles, re-synced and checked the steps and multiplied the number of steps by the inches in my steps for running and it was quite close. It should be of note too, that I calculated my step length for running and walking quite precisely by measuring out a distance with a tape measure on the lawn and counting how many steps I took during the distance, and then calculated by step distance from that.  I did that for both walking and running and twice to average my results.

Some members of the Fitbit community have tried using their Fitbit Flex for things in addition to walking and running, like for logging biking and time on the elliptical as well as with things like Plyometrics, Yoga, stretching, and weight training.

Of course the Fitbit Flex was not meant to log these things, so you can’t exactly expect accurate results or even consistent results among varying people, if at all for some activities.  Though Some have fairly good luck with it logging a certain amount of calories during this or that exercise, but usually towards the caloric low end.  Things like using the elliptical provide better results, as I found – it was nearly comparable to walking miles, but still a bit low.

JumpAfter doing an hour of P90X Plyometrics (you can read my review of the P90X DVD series versus some other popular workout systems in this blog post) the Fitbit Flex measures 4,320 steps, 363 calories, 2.08 miles, and 22 active minutes.  If you’re not familiar with P90X it is a series of somewhat advanced exercises of all types as well as weight training, yoga, and stretching and even a little martial arts.  Plyometrics is an interval-oriented jump-training exercise.

There are many things that would make the Flex count steps in Plyometrics of course, but despite that the calories were still on the very low side.

Fitbit User LEN (an avid bicyclist, to say the least) gave some interesting advice on the Fitbit activity forums, mentioning that the Fitbit works great as a cadence counter, and at least for him was within 2% of what his Garmin was giving him for cadence.  He also says to double the steps count to get something more accurate for counting actual steps.

Android App

The Android App

It sounds as though results of using the Fitbit series to track something that they aren’t made for, like cycling, depends on the Fitbit device model and perhaps the person/bike as well as other factors.  

The Fitbit Flex is made for tracking steps, and indeed that’s where it shines – so your results with tracking other activities will vary.

I think the sleep tracking works well, though it may be a bit subjective.  It’s interesting to check the stats on restless time, wake time, etc though without a sleep lab I couldn’t say how accurate any of it really is except to say that I know when my sleep efficiency is shown as low very then very likely I indeed can feel that I did not sleep well.  This general feeling has been off a few times where I felt like I got a good night’s sleep despite a dip in efficiency as shown on the Fitbit site, and vice versa but for the most part it seems to correspond to how I feel when I wake.

So that’s about it when it comes to the functioning of the Fitbit Flex device itself.

The real power of the Fitbit is in the website and apps.  As I mentioned earlier in this post you can set all options, settings, and privacy and of course, most importantly, you can see your stats.  


The Fitbit Flex Dashboard

The Dashboard is probably going to be the place you go to the most, or the place you start at, and it’s where you can see more precise measurements of your steps, calories, mileage, how you are stacking up against others, and where you can click the ’tiles’ (which, BTW, can be changed around and edited and deleted to your personal preferences) and get much more detailed info on each tile category, or change goals or manually add things like activities, food, water intake, etc.  You can also click the LOG menu option across the top of the Dashboard screen to access each section – Food, Activities, Weight, Sleep, Journal, Heart, BP, and Glucose.  Any of these can be used to manually enter data as well as to see the results from the Flex and/or from your manually entered data.  


Of course, things like food, weight, journal entries, heart-rate, blood pressure, and Glucose must be manually entered unless you have a compatible device like the Fitbit Aria Wi-Fi Scale or are receiving synced data from other connected sites like MyFitnessPal or Endomondo.

 Food Logging

A note here – if you track your food you might want to consider using MyFitnessPal synced to Fitbit as the food entry on MyFitnessPal is a bit more advanced than on Fitbit, though that works fine and has a lot of various foods in it’s database.  

If you want to sync your Fitbit to and from Garmin Connect there is a site called  Unfortunately it has not been working for me and I was not able to contact the programmer.  This worked well as any walking, running, or anything else you logged with your Garmin would take precedence over the steps logged with your Fitbit so there would be no overlap – that’s providing you are wearing the Fitbit at the same time of course.

Since that is not working for me (let me know if it works for you!) I connected Fitbit to Garmin Connect in a roundabout way – by using Endomondo as an intermediary – unfortunately if you’re using your Garmin GPS watch to log anything non-GPS relate dlike your indoor cycling, treadmill running or walking, elliptical, etc Endomondo won’t import it.  

If you’re familiar with my blog postings you may have seen my posting on fitness syncing sites and connecting them together as well as my post on exercise/fitness logging sites.

garmin forerunnerSign into Endomondo or create an account, and go to the Connect settings under Settings below your name and connect Endomondo to Garmin Connect and Fitbit on that screen.  

The stats and bar graphs can take a little getting used to but you’ll find plenty of data both in number form as well as bar graphs, mousing over them gives you more info.

It’s good, and useful but could be better.  You can get a general idea about your stats and numbers.activity

But for a bit more luscious bar graph action head on over to and give permission for the site to connect to your Fitbit stats (you seem to have to do this every time you use it, good for security I suppose).  You won’t be disappointed if you like your stats and graphs…

For even more precise numbers that you can crunch yourself, import into a spreadsheet, or if you want to back up your Fitbit data but don’t want to pay for the Fitbit Premium Account – there are alternatives.  It’s a bit complex but you can set up a real-time data import into Google Drive (may or may not work at this point) or better yet just use this site – FitBit Data Export.

Along the same lines – there are some interesting Fitbit apps that give you a bit more data or allow you to do this or that that the official app doesn’t, including some for finding lost Fitbits (the IOS one – there are more and Android app like this one – there are more of these too)Dashclock extensions for Android, Android Home Screen Widgets, among many other things.

BTW, click here for a short promo video from Fitbit.


If you’re looking for a well-established, well-supported activity and sleep monitor that works well and is reasonably accurate then the Fitbit Flex might be for you.  While there are alternatives, some with more features, including those from Fitbit itself, it’s hard to beat the simplicity of the functioning of the Fitbit Flex and the ability to quickly check your stats on the website or apps.


I wanted to thank the people at Fitbit for their excellent media kit and permission to use screenshots and their logo in this blog posting.

 Update 2017 – Fitbit has released a new Fit Flex 2, check it out here.

Marc M

I am a web developer and fitness geek, but I have a heck of a lot of differing interests.  Biking, the Internet, technology, movies, fitness, running and walking and hiking, science fiction, photography, graphics, WordPress, flying and aircrafts, pets and animals, history, and much more.  I like to stay very fit but I don’t mind sitting at my computer for work and play either.  I live in upstate New York (that’s far from New York City) in a rural area, yet close to a small city, with my beautiful awesome wife, a bunch of beloved cats and dogs and chickens in a very old multi-century house.


  1. Certainly, here’s a simplified chart outlining the pros and cons of the Fitbit Flex:

    Pros of Fitbit Flex:

    Activity and sleep tracking.
    Wireless syncing.
    Long battery life.
    Compact and lightweight.
    User-friendly mobile app.

    Cons of Fitbit Flex:

    No display on the device.
    Limited features (lacks heart rate monitoring and GPS).
    No altitude tracking.
    Relies on your smartphone’s GPS.
    Design may not be stylish for some.
    Limited compatibility with certain devices.
    Potential accuracy issues, particularly for non-step activities.
    if you want detailed information check this website

  2. I really liked your blog, there was a lot of information in it. I’m a blogger myself, so it would be great if you could check out my blog too.
    Here are some pros and cons according to me.

    Slim and Attractive Design: The Fitbit Flex 2 is a beautiful and discreet tracking device that can be used as a bracelet or a wristband due to its slim and sleek appearance.

    The waterproof: Is one of the few Fitbit models featuring a fully waterproof design, which is users can wear it in the bathtub, in the shower, while swimming, or during other activities that involve water.

    Basic Activity Tracking: The Fitbit Flex 2 tracks essential health information that promotes a healthy lifestyle, including footsteps utilized, distances journeyed, burned calories, and active minutes.

    Smartphone Notifications: You may remain engaged when you’re on vacation using this function, which offers vibrations and bright lights to phone calls and text notifications.

    No Display: The Fitbit Flex 2 lacks a display screen, thus in order to read your fitness data, you must use the Fitbit app or look at the LED lights.

    Lack of Built-In Heart Rate Tracking: For individuals who wish to monitor their heart rate when working out, this model’s lack of heart rate monitoring may be a drawback.

    Limited Battery Life: Compared to certain other Fitbit models, the battery life is somewhat limited & requires more frequent charging. It might call for a charge every few days.

    Basic functions: The Fitbit Flex 2 has some basic fitness tracking activities, but it lacks some advanced capabilities seen on more advanced Fitbit devices, such as GPS and comprehensive sleep tracking.

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