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Polar M400 review: A feature-packed GPS running watch that can also track your steps and sleep

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The Good The Polar M400 has good battery life, can sync wirelessly with your phone, includes GPS and activity tracking, charges through a normal Micro-USB and supports wireless heart-rate monitors. It also has automatic sleep tracking, an always-on display with a backlight, inactivity alerts and is waterproof.

The Bad The big design may not be appropriate for all environments. There's no vibration for alerts or a silent alarm.

The Bottom Line The feature-packed and waterproof Polar M400 offers a good set of features for beginners and advanced runners a like. It also provides feedback on your daily activities and sleep.

7.4 Overall
  • Style 7
  • Features 8
  • Ease of use 7

Editors' note, December 23, 2014: The original review was of a pre-production unit of the Polar M400. We originally had problems with the signal strength and accuracy of the GPS. Additional testing has shown that these problems have been resolved in the retail model. As a result we have increased our rating from 3 stars to 3.5 stars.

Editors' note, December 31, 2014: Polar's Flow app has been updated on Android with support for the M400.

Polar's latest watch looks to further bridge the gap between activity trackers and GPS running watches. The Polar M400 is the company's second GPS watch that includes tracking for things like steps taken, distance traveled, calories burned and sleep. Unlike the more expensive V800 multisport watch, however, the M400 retails for £135 in the UK, $200 in the US and AU$249 in Australia, which puts it in line with similar products on the market.

The watch, which can be had in either white or black, can also be bundled with a heart-rate monitor, although this will increase the price to £170, $250 and AU$299. If you already own a chest-based heart-rate monitor, even if it's a non-Polar monitor, it should work just fine as long as it supports Bluetooth LE (low energy), also known as Bluetooth Smart. A Garmin heart-rate sensor isn't compatible, though, Garmin uses ANT+ technology.


The M400 is slimmer than other running watches, but not nearly as discrete as say the Microsoft Band . It utilizes a rubber watch strap with a security loop to sit snug on your wrist. The strap is quite soft, which makes the watch comfortable to wear, despite being so large. Don't get me wrong, though, you can still feel it on your wrist. It's not like other activity trackers, such as those from Fitbit or Jawbone, that are small and lightweight, although as far as running watches go, it's relatively comfortable.

Sarah Tew/CNET

The M400 measures 11.5mm thick and comes in at just over 56g, making it slightly heavier than the similarly priced Garmin Forerunner 15. The Garmin, however, had a cheaper and more plastic feel.

On the back of the watch you have a small rubber flap that covers a microUSB port. It's really a blessing that Polar included a Micro-USB for charging, rather than some sort of proprietary dock connector. A cord is included with the watch, which you can use with your computer or smartphone adapter as long as it outputs at least 500mA at 5V.

Sarah Tew/CNET

The port itself is actually quite interesting. You would expect the reason for the flap is to protect the port from water and while that's true, it's not the end of the world if it gets wet. The microUSB port on the M400 is actually internally waterproof (as is the watch itself) up to 30 meters, so yes you can shower and even go swimming without taking it off.

On the front of the watch there are five buttons: two on left and three on the right. The top left button activates the backlight, while the bottom left is the back and end button. The top right is for scrolling up, the middle is to select and start activities and the bottom right is for scrolling down. Some of these buttons also have secondary uses. For example, holding the top left button will enable a button lock and holding the bottom left button will sync the watch, while a long press on the top right button will scroll through the different watch faces.


The M400 has a plethora of features. While you won't see any smartphone notifications on your wrist, it can track your active time, the steps you take, distance you travel, calories you burn and your sleep at night. The GPS and other sensors gives it an extra boost, allowing it to track your distance, pace, time and altitude while running. Add in a Bluetooth heart-rate monitor and you can even track your beats-per-minute. The watch is very smart. In fact, it knows when it isn't being worn, when you are sitting, standing, walking, jogging or resting.

Sarah Tew/CNET

Speaking of running, the experience is quite enjoyable. The watch includes all the features you would expect from a running watch, with some added activity bonuses thrown in on the side. It will automatically pause when you stop running and automatically record a lap at one mile or kilometer. You can also create interval workouts based on time, heart rate or distance.

Many of the GPS running watches on the market today include a virtual pacer feature that will help keep runners on track to run a certain time. In lieu of that, the M400 includes a finish time estimator that, rather than telling you that you are running too fast or too slow, will tell how long it should take you to complete a set distance at your current pace. There is also a "back to start" feature that will help compass you back to your start point, an incredibly helpful tool for running in unfamiliar neighborhoods.

Something that annoyed me was that when I would pause a run, it wouldn't let me see any of my run stats. The only thing you are shown is the amount of time you have been running. It can be frustrating, but it isn't a deal breaker.

The M400 gives you a considerable amount of information during and after you have completed your run, all of which is displayed the devices 128x128-pixel resolution black and white display. You can view the start time, duration, distance, calories burned, fat burn percentage of calories, average pace, max pace, max altitude, ascent, descent, auto lap times, best lap time and average lap time. It will also keep track of your personal records and will notify you after you complete your longest and fastest runs. In comparison, the Forerunner 15's post-run information only displays the duration, distance, pace, calories burned, laps and any new personal records.

Sarah Tew/CNET

The M400 can store up to 30 hours of past runs on its internal storage. All of this information can also be uploaded to Polar's website and mobile app using your computer or connecting your smartphone over Bluetooth, a feature, much to my dismay, Garmin didn't include with the Forerunner 15.

As I mentioned earlier, the heart-rate monitor is chest-based. While it would have been nice for a wrist-based optical heart-rate monitor, similar to the Adidas MiCoach Smart Run , Microsoft Band and Fitbit Charge HR, chest-worn straps tend to be more accurate.

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