Fitbit Flex Wireless Activity and Sleep Wristband REVIEW

September 8, 2013
4 mins read

4 Stars


This body monitor makes up in general usefulness what it lacks in absolute accuracy, says Ashley “Actionman” Kramer.

ACTIVITY MONITORS ARE nothing new. After all, basic pedometers measuring how many steps a person takes have been around for hundreds of years, but technology has really extended the possibilities of this category. Some modern units are aimed at athletes and use GPS to track performance on runs or bike rides. Fitbit’s Flex, on the other hand, is designed to be a motivational tool, encouraging more mainstream users to get and stay active.

WDF-Fitbit-FlexThe heart of the Flex is a tiny plastic sliver that slips into a silicone wristband (small and large bands are available in different colours). The band is light and unobtrusive enough to be worn all day, and indeed all night, which is handy given the Flex’s multi-purpose focus. The Flex uses a three-axis accelerometer to measure motion and uses that information to calculate calories burned, distance traveled, steps taken, and even sleep quality – no movement translates into good sleep (more on this later). There’s also a vibration motor stashed in there that is used to power the silent alarm.

The onboard display is limited to a series of bright LEDs that are used to indicate battery status, charging, daily progress and mode. This means that the bulk of interaction with the Flex will be done via computer or smartphone. A small USB cradle is supplied, which allows the Flex to be connected to a computer for downloading and charging purposes. It’s also equipped with the new low-energy consumption Bluetooth 4.0 standard for wireless synching. This limits its compatibility to newer models of phones – think iPhone 4S or Samsung Galaxy S3 and you’ll have an idea of the type of compatible devices.

The actual Flex is this thing - it just slots into the wristband
The actual Flex is this thing – it just slots into the wristband

I paired the Flex with a MacBook Pro without too much hassle once I’d downloaded the software from the Fitbit site, and with a review Samsung Galaxy Note 8.0. In both cases, connectivity was reliable and fast. Both interfaces are user friendly and intuitive to use, allowing a fair degree of customisation if users so choose, but it’s also possible to be up and running (so to speak) in short order. The Lithium-Ion battery promises five days of battery life and I found that it got to four days without too much hassle, but I always elected to charge it at that point rather than risking it going dead while at work – you can’t just plug it into a random PC, you need to have the cradle with you.

In use, the Flex proved to be consistent rather than accurate. On days that I’d been really active, it reflected that and on days where I’d been slack, it showed that too, but the distances it was measuring were the stuff of myth. Checking the approximate distances between the office and Britomart and the office and Food Alley on Google Maps while allowing for some error for the other general walking around I did showed that the Flex was overestimating distance by at least 50 percent. Given that it’s wrist mounted, it picks up every movement and while the sensors and algorithms should be able to differentiate walking from weight lifting, for example, I suspect that much of the movement is counted as steps, which translates into distance.

Still, that’s not a big deal given the Flex’s intended market and purpose. If a user walked 10,000 steps a day last week and 20,000 a day this week, then they’re being more active. If they drop back to 10,000, they’re being damn lazy, and the Flex’s social sharing functionality will let their Fitbit-using friends see that fact. This will hopefully drive said user to new levels of activity, which is after all the point of the exercise. The Flex also tracks very active minutes, calories burned (again an approximation but a consistent one) and the software offers a log function to help set up a food plan, and manually monitor parameters such as weight, water consumption, blood pressure, glucose, etc. So, it really is ideal for folk who just want an incentive to get active and a way to monitor that activity and associated lifestyle factors.

The Flex also tracks sleep quality. Tap the unit twice and it drops into sleep mode, monitoring how well you sleep by your movement patterns. Once again, the Flex seems to be consistent rather than accurate. According to the readout many mornings, I slept like a baby with up to 99 percent “sleep efficiency”. That’s not true, nor has it ever been true, even when I was a baby. However, on the nights when I slept reasonably well, the Flex showed me to be dead to the world and on nights when I didn’t sleep all that well, the graphs indicated that I was more restless, so it’s useful in tracking sleep in a general way and for getting an idea of what helps and hinders good sleep.

The silent alarm is a neat function – it’s set in the software or app and uploaded to the unit. At the given time, the Flex vibrates like crazy; it’s more than a little disconcerting to be woken up that way the first time but I soon found it to be better than the screech from my iPhone (bearing in mind of course that if you need to be regularly woken up by an alarm, you’re not getting enough sleep).

WD-Fitbit-FlexSo all in all, Fitbit’s Flex is best seen as an indicator rather than a precision instrument, but it does the job nonetheless. Just like one of those silly scales that measure bodyfat, it doesn’t have to be hyper accurate as long as it’s consistent. As the company puts it, this device is designed to make fitness fun and a lifestyle; it’ll certainly do that. Unlocking achievement badges, sharing with friends and linking to a number of popular fitness and weight loss apps makes it perfect for the target market, so I won’t mark it down for its lack of precision. At the price, the Flex is well worth a look for those who need an occasional prod to get out and about. ASHLEY KRAMER


  1. Me ha llamado la atencion , la nota, efectivamente muy buena, gracias
    por la advertencia, muy informativa. Sigo fizgoneando por la web a leer mas
    notas aclarativas, merci again.

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