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(Pocket-lint) - Casio's position in the world of Wear OS smartwatches is pretty unique. It's carved out a little niche, by building smartwatches with dual-layer screens, hefty yet durable designs, and heavy marketing towards the outdoorsy types.

These are smartwatches for adventurers, hikers, and people who'd rather be out on the mountains, in forests, or paddling in kayaks, than hipster fashionistas who want sleek and stylish wristwear. 

With the WSD-F21HR, Casio is seeking to be even more useful to that group of people, by also offering a built-in heart-rate sensor; something that, until now, has been lacking on its outdoor sports-focused watches. 

Chunky monkey

  • 61.7 x 57.7 x 16.8mm; 81 grams
  • Waterproof to 50 metres
  • MIL-STD-810G durability
  • Resin bezel

If there's one thing you can count on from the WSD-F series, it's that the watches have a very chunky, outdoorsy style. That's to protect the innards and screen from the elements.

This Casio's screen is surrounded by a durable and strong bezel with a significant protrusion to ensure that if you do clatter the watch against the side of a rock (or a door handle when you're at home), it'll not impact the screen. It's made from a resin, to keep the watch as light as possible, and you can definitely tell. While bulky, the watch doesn't feel as heavy and clunky as some other Casio outdoor watches that we've used. 

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As a point of comparison, it weighs around 81g, which is about 10 grams lighter than the WSD-20, and a couple of grams lighter than the WSD-F30, the latter which is actually smaller. 

Still, the F21HR is noticeably heavier than an Apple Watch or Garmin Fenix 6 Pro, but it doesn't take too long to become accustomed to wearing it daily. We just don't think it's anywhere near sleek enough to make use of Google's sleep tracking features within Google Fit. 

The one thing this particular design does fantastically well is deliver on durability. Casio's Wear OS watches are all compliant with MIL-STD-810G US military standard durability, and that essentially means it'll keep working even when the temperature drops to -10C, and is water-resistant up to 50 metres. It'll also almost certainly survive any impact it faces in your daily adventures. 

The watch features three buttons on the side, which are really easy to find and use. And, while the watch bezel has labels on it to dictate what the default function of those buttons is -  Map/App launching by default - Wear OS will allow you to programme the top and bottom buttons to do what you want. So if you want the bottom watch to launch Google Fit, or the Weather app, you can. 

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Those who like to customise the style of their watches by changing up straps every once in a while will be disappointed, sadly, because Casio hasn't built that capability into this watch. The strap is a durable, soft urethane band which fits and holds well. It feels really durable, and the fact that the clasp holding it to your arm has two prongs rather than one means there's less pressure than a single-holed one, making it less likely that you'll rip it under stress. This is a much nicer strap than the one found on the WSD-20 predecessor.

Dual displays

  • 1.32-inch dual display
  • 320 x 300 TFT primary display
  • Monochrome LCD secondary
  • Flat tyre - not full round

The one feature that's set the WSD-F series apart from its smartwatch competition is the dual-layer display tech. Unlike almost every other smartwatch on the market, it combines a standard colour screen with a second, digital monochrome LCD panel. Using this combination, it can display the time constantly while using very little battery. That means you get the standard smartwatch stuff, but still have a practical digital watch on your wrist at the same time. 

This secondary display simply shows you the date, the time and the battery level when being used as a timepiece, but will also show other data if you're in the middle of an activity. Its only customisation choice is whether you want a bright background and black numbers and text, or white characters on a black background. 

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As for the primary display, that's a colour TFT panel, which means you don't get as vibrant a colour performance or deep blacks like you would on the OLED-based panels you find on a lot of other modern smartwatches.

This, plus the 'flat tyre' black bar portion at the bottom of the screen is what sets it apart from the WSD-F30, which has both a full round OLED display to make it more punchy and vibrant. 

That's not to say the F21HR has a bad screen. Colours might not pop, but they are vivid enough, while the resolution is sharp enough to enable some fine details to be seen. However, it's not as pixel dense as the significantly sharper screen on the WSD-F30. 

What we've long-loved about Casio's screens is how they utilise it to build interesting and useful watch faces. Many of Casio's are location- and activity-focused, so many automatically build a map of your current location in the background as the wallpaper while also showing complications with useful data. 

Fitness tracking

  • Casio Moment Setter app
  • Heart rate monitor and GPS
  • Manually sync with Google Calendar/Fit

Somehow, surprisingly, this watch is Casio's first outdoor/sports-focused smartwatch to include a heart-rate sensor. It's the one major thing missing from the previous two, so thankfully that's now been rectified. 

It means that when you track a run, walk or other activity using the Moment Setter app (or any other third-party sports app) you'll get to see how your heart rate changed over the course of the activity. That combined with GPS and all the other sensors gives you get a fuller picture of your activity. 

Other sensors include an air pressure and altitude sensor, as well as accelerometer and gyrometer. 

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If there's one thing that can be said of the Casio Moment Setter app, it's that it makes data really clear and easy to read. Whether you're using the primary colour LCD display, or using the secondary monochrome screen, it offers easily visible and easy-to-understand information whether you're running, cycling or hiking. 

Where it has fallen short in the past, and still does to an extent, is what happens to that data when you've finished the workout. There's no real companion app that it syncs to on your Android phone or iPhone, and so there's no easy way to see your performance on a big screen. With that said, there's a sort-of workaround. Digging into the settings on the watch, there are two options you can enable to make syncing and viewing your activity afterwards much simpler.

It's possible to activate the ability for it to share the activity with Google Fit, syncing the activity with Google's default activity/fitness tracking services, which will then be available to view on the app on your phone afterwards. With this syncing/sharing method you'll get key information as well as a map of your route.

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The one issue we found with the actual fitness tracking was that the GPS was a little slow in finding our location at the beginning. Comparing with the Apple Watch Series 4 alongside it - which we've found to be quick/reliable - the end distance was noticeably different. Even on the 25 minute easy run (shown above), there was a good 130-150m difference in tracked distance, which inevitably led to pace being off by about 20 seconds per kilometre. Heart rate was pretty accurate though, with averages showing about 4bpm different between the Casio watch and Apple device.  

You can also give the F21HR access to your Google Calendar account, and enable auto-exporting to ensure that any and every activity saves as a simple text file on your calendar, then go back to it any time to see your basic metrics. It'll show you simply how long you worked out, how far you went, your pace, and other important bits of data. Sadly, with the calendar exporting you don't get a map to view your route. 

Battery life, features and performance

  • 1.5 days as a smartwatch, one month as mono only
  • Up to 20 hours of GPS use
  • Charges in 2.5 hours

Judging battery life on the Casio is something that's difficult to put an exact figure on, primarily because it depends on how you use the watch. Using it in the same way we'd use any typical smartwatch, checking the time and notifications a few times a day and maybe tracking a 30-40 minute activity using GPS and heart-rate monitoring, the WSD-F21HR comfortably got through a day without worry.

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A big part of this is because of that monochrome display. It uses a lot less power than the main screen. To the point where - in our particular use case - we actually got through two work days using the watch. It definitely didn't need charging every day, and on some lighter use days with no exercise and few notifications, it had barely dropped below 80 per cent from being fully charged in the morning. 

Whichever number you end up with in battery tests, the short version of the story is that Casio's watch lasts way longer than most other Wear OS smartwatches because it regularly switches off that primary screen. 

When it runs flat, you charge it using Casio's proprietary connector which we don't find the best. It's a cylinder-shaped connector that snaps onto a magnetic port on the left side of the watch. The downsides are that the magnet isn't particularly strong, so can easily become disconnected with a slight knock. It's also pretty slow to charge up the watch, taking up to 2.5 hours, which is long when you think there are phones out there with much bigger batteries that can fully charge within 40 minutes. 

Like any Wear OS watch, you can install third-party watch faces from the Google Play Store, as well as download Wear OS compatible apps. For instance, if you wanted a running tracker that synced with a smartphone app, just download Strava or something similar, and it'll give you the same capabilities as any other smartwatch. Of course, you can reply to notifications from some apps, and glance at the Google Assistant screen to see a rundown of your upcoming day. 

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The only thing it's really missing as a smartwatch is NFC payments. This Casio doesn't have NFC, so can't make use of Google Pay for contactless payments in stores with contactless terminals. We feel this is a feature necessary in any modern smartwatch, so it's a shame to see it missing here.


Casio has successfully built another watch that's designed for the outdoors; for runners, hikers, paddlers and cyclists. It's durable, has great battery life and a genuinely useful dual-layer screen. Only this watch, finally, brings heart-rate monitoring.

The Moment Setter watch app is really great too, as long as you're happy with the relatively limited number of sports offered in its tracking. With that said, it's still missing a smartphone companion app for better integration with your smartphone, although you can now export and sync data with Google Fit, which is genuinely useful. 

The long and short of it: if you want a solid, durable outdoor smartwatch, the F21HR is definitely Casio's best effort yet. We think it's still got a little way to go before it's as easy to recommend as something like the Garmin Fenix 6 range, which lasts longer and has much better smartphone integration. 

Also consider

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Casio WSD-F30


It doesn't have the heart-rate monitor of the F21HR, but it does have a fully round OLED screen, and is smaller too. It also has longer battery life and a higher-resolution primary screen. What's more, now that it's older, it's really not more expensive either. 

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Garmin Fenix 6 Pro


Garmin make some of the best smart outdoor sports watches around, and the Fenix 6 Pro is the pinnacle of that effort. It's sublime in almost every way, and syncs activities automatically with its own Connect app - which is one of the best mobile apps around for fitness tracking and metrics. 

Writing by Cam Bunton. Originally published on 9 March 2020.