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Polar M400 Review



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  • Tracks GPS, heart rate and daily fitness
  • Slim and light for GPS tracking
  • Excellent features for price


  • No underwater heartrate monitoring
  • No route navigation
  • Chest belt needed for heart rate

Key Specifications

  • Review Price: £169.50
  • Daily activity fitness tracker
  • GPS activity tracking
  • Wireless heartrate monitoring
  • 8hr battery for GPS and HRM tracking, 24 day battery for fitness tracking only
  • 30m water resistant
  • Slim (11.5mm) and light (56.6g)
  • Highly configurable

What is the Polar M400?

The Polar M400 is one of a new breed of fitness wearables – combining the simplicity of fitness bands such as the Fitbit Flex with the heartrate and GPS activity tracking of high-end running watches such as the TomTom Runner Cardio in one device. And all at a price that is closer to a fitness band than GPS watch.

The result is a device that’s surprisingly functional, particularly when you consider it costs barely more than a higher-end fitness band – if you already have a Bluetooth chest strap, it’s £30 cheaper still. It lacks one or two notable features, but it’s a great option for anyone buying their first proper running watch.

See also: Apple Watch Review
Polar M400 watch and heart rate sensor on wooden surface.

Polar M400 – Design and screen

The first and foremost thing about the Polar M400 is that it’s incredibly slim (11.5mm) and light (56.6g). It is no more arduous or bulky to wear than most fitness bands and is certainly less obtrusive than just about every other GPS-tracking watch on the market.

Quite where its antenna is hidden is unclear, but it’s vital it doesn’t get in the way when you’re wearing a fitness band day and night. The Polar M400 gets this right more than any other rival. That also means that it works better on skinnier wrists. Again, this is in stark contrast to key rivals.

The light weight and low profile may be to its credit, but elsewhere it is perhaps too unobtrusive – and borders on plasticky. The 128×128 pixel, 33mm screen may not set a smartwatch fan’s hair on fire, and the resulting info screens are bereft of design flair or interest. But at least everything’s bright enough to be visible even in fairly direct sunlight and, there’s loads of information on display. There’s a backlight for those late evening runs, too.

The five buttons (up, down, select, back, light) all work well and are designed so you don’t trigger them accidentally. On the back, there’s a micro-USB socket – which means you can travel with one phone and watch cable to charge. You can sync via Bluetooth to a smartphone app if you prefer. The socket is rated to 30m water-resistant without its cover, which may turn out to be important.

If there is a let-down to the Polar M400’s design, beyond its blandness, it is that both the USB cover and main watch strap – made of similar material – seem worryingly flimsy. It’s that kind of slightly cheap plasticised rubber that can be prone to brittleness.

There was no sign of any tearing, stress or breakage in either during testing, but the combination of the design of the clasp and the rubber may give rise to concern long-term. That said, pins hold the strap in place, so it’s clearly replaceable, and the USB socket is waterproofed without its rubber cover.

Related: Best Fitness Trackers and Activity Trackers

Polar M400 sports watch on a wooden surface.

Polar M400 – Features

The key thing to understand about the Polar M400 is that it functions as a fitness band and activity tracker.

As a fitness band you wear it non-stop and it tracks steps and sleep like rivals. Unlike many fitness bands, it even works out automatically when you’ve gone to sleep – you don’t need to tell it “night night”.

Like the Polar Loop, if paired with your phone (via Bluetooth), the Polar M400 will also send inactivity alerts to your phone and wrist, reminding you to get out of your seat and jump around if you’ve sat still for too long. You then have a few minutes to move, or you get a bad mark in your daily diary in the app.

Buy Now: Polar M400 at from £117

So far, so fitness band. But press the central button on the watch and you’re into a menu of potential fitness activities. Choose an activity and hit start and the GPS signal from the watch, and any heartrate data from a compatible Bluetooth HRM strap, will be logged until you stop. With eight-hour GPS and heartrate-tracking battery life, nearly all likely fitness activities can be tracked.

In choosing an activity, you select from a list of “sport profiles”, with the ones displayed on the watch selected via the Polar Flow site. This ensures Polar’s customised calorie counter is highly accurate.

There’s a wide range of profiles to choose from, ranging from “Aqua fitness” to “Classic roller skiing” and “Yoga” – enough to ensure you can get a fairly accurate sport profile for just about anything you do.

Related: Polar H7 Heart Sensor
Polar M400 watch on wrist displaying cycling start screen with GPS signal.

The sport profile you choose also dictates what information you see (customisable from the Flow site) and what’s turned on – obviously, if you’re on an indoor rowing machine, there’s not much point wasting battery life on GPS.

As well as setting up sport profiles on the Flow site, you can also custom-rig your heartrate zone and, brilliantly for a watch this price, set up complex interval workouts as a “favourite” or in your diary. These mean you can configure warmup and cooldown periods and set conditional targets, such as staying within certain heartrate zones for a certain time or distance.

On the watch itself, you can do a 15-minute “fitness test” that gives you a very accurate measure of your V02 Max and get a “running index” score at the end of each run that – based on age, gender, your speed and heartrate – ranks your performance. And you can trigger laps, or set up auto-lap conditions.

On top of that already impressive feature list, there’s 30m water-resistance. Sadly, in-water heartrate monitoring isn’t available – unlike in the higher-end Polar V800.

Also out, compared to the Polar M400’s more-than-twice-the-price sibling is recovery status, navigational routing (there’s only a simple “return to start” compass pointer) or cycle-accessory support (power, cadence etc.). New-fangled in-watch optical heartrate monitoring isn’t in either – meaning you need to wear a wireless Bluetooth strap. Again, at this price, those are hardly expected. There is, though, foot cadence via the footpod, for indoor running.

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