- Customizable watch faces
- Offline map support
- Very durable
- Works well with some third-party apps
- Very bulky
- Tracking data not stored
- Poor screen visibility
- Fitness tracking is limited
We're now into multiple iterations of the Pro Trek smartwatch and while it has vastly improved as an adventure companion over time, there are some aspects of the series we've remained critical of.
One of our biggest gripes has been the absence of a heart rate monitor, something you can find on most sports watches and smartwatches these days.
Essential reading: Best outdoor watches to buy
But with the F21HR, we are finally getting that heart rate monitor that dishes out real-time data. Its addition could give the latest Pro Trek more appeal to trail runners who prefer eating up those training miles in more challenging terrain.
Priced in at , the F21HR comes in at the same price as the Casio Pro Trek Smart WSD-F30 we reviewed earlier this year. So you're not paying a premium for the addition of heart rate.
So should the new Pro Trek Smart be your outdoor watch of choice? We've been putting it to the test to find out. Here's our full verdict.
Casio Pro Trek Smart WSD-F21HR: Design
The first thing we should say about the F21HR is that it isn’t the natural successor to Casio’s most recent Pro Trek, the WSD-F30. It's actually the follow-up to the WSD-F20 Pro Trek we reviewed back in 2017.
What that means is that this watch lacks some of the improvements made on the F30. The most significant thing is the size of this device. The F20 was a beast of a watch and sadly that's also what you get with the F21HR. For an outdoor watch used for hiking that’s not really a major issue, but for something designed for fitness, it's more of a problem.
For running, you do gradually get used to its hulking size, but it’s always a noticeable piece of hardware on the wrist. Using it in the gym is a no-go, especially if you’re doing exercises that use equipment like kettlebells or dynamic barbell movements.
You’ll end up just taking it off because it keeps banging against something or you can’t mobilize your wrist correctly in a movement.
And when used for running or HIIT workouts it becomes instantly clear that it’s not a piece of kit for speed.
At 81g, it’s still 12g lighter than the Garmin Fenix 6X (93g) and the lightest of the WSD range to-date, but feels bigger due to the overall bulk of the unit.
It comes in two design variants: you've got your pick of a black or red bezel, neither of which we like as much as the orange and blue of the F30 model. However, the design hasn’t changed a great deal across the previous iterations, so if it’s a look you like, then you’re unlikely to be disappointed.
You’ll also be pleased to hear there’s still the bold feature labels positioned around the face: tool, map, sensor and GPS.
That rugged, chunky design isn’t just there for looks though. As well as 50-metre water resistance, it also incorporates military-grade protection (MIL-STD-810G) – which you don’t see very often on a fitness watch.
It still incorporates the glove-friendly three-button operating system, used in conjunction with the touchscreen display. The left side is where you'll find the sensors as well as the proprietary Casio magnetic charging point – unfortunately that charging point hasn’t seen an update and still suffers from falling out at the slightest knock.
The screen is the same 1.32-inch dual-layer display used on the F20 that incorporates a 320 × 300 pixels color TFT LCD screen as well as a monochrome LCD option.
In most lighting conditions the color LCD screen will do the job and the quality of the screen is one of the best we’ve seen. However, it does struggle in extremely light conditions; making it hard to see the screen – something that was vastly improved on the F30.
Casio Pro Trek Smart WSD-F21HR: Wear OS
As mentioned, this is another Casio that runs on Google's Wear OS, giving you the full gamut of Wear features including notifications, Google Assistant support and the ability to download apps.
Read this: Best Wear OS apps to download first
For a standard sports watch user, Wear OS can be a bit confusing and it takes some time to get used to the logic of the operating system and where things live on the watch. But if you're willing to put that time in, it's a largely intuitive platform that has come on leaps and bounds in recent years.
There are watch faces too, with a number already available on the watch itself as well as an enormous amount downloadable from the Google Play store. The biggest difference on that front is that there are now heart rate specific watch face designs, making it easier to glance at your HR data.
Casio continues to include its apps to make it better suited for outdoor pursuits and the F21HR benefits from an enhanced version of Casio's Activity app. That app now offers profiles for running and trail running. You can also now customize the data shown in those running profiles to include heart rate.
The other main apps that you'll want to get to grips with are Extend Mode and Multi Timepiece, as well as a very nice little app called Moment Setter. The latter enables you to customise notifications using the sensor information available.
Again, it’s a feature that only applies to the serious outdoor-type. But the ability to set alerts when you’ve reached a certain elevation, you’re leaving a designated perimeter or that it’s going to get dark in an hour, are really useful for those hitting remote destinations.
Casio Pro Trek Smart WSD-F21HR: GPS and mapping features
GPS is, for an outdoor watch, one of the most important factors. Whether that’s for safety or for map accuracy, you want to know that the device is taking you on the right route.
The watch comes with two map options built into the software: Google Maps and Mapbox, and pops up instantly by pressing the top button on the watch. You will however need a data signal to use maps on the fly. If you’re out in the middle of nowhere you’ll need to download these before you head out.
You can download maps of up to 50km via the watch and, for our money, the Mapbox options are far superior to Google Maps for isolated locations. You can have up to five maps downloaded onto the watch at any time, which should be more than enough.
It does take a bit of time to get used to the GPS mapping features of the watch. The screen size is one of the best in terms of visibility and size, but pinching and scrolling through the maps is never going to be easy via a watch.
Once you’ve set your navigation point and got used to the format, it does get easier though and is far by one of the best tools we’ve ever seen on an outdoor watch.
If you want to take your experience up a notch we’d advise downloading the ViewRanger app. Not only does it utilize Ordnance Survey maps (an essential in our view) but also gives access to a massive range of user-generated routes to use yourself. They even come with explanatory notes to keep you on the right track.
Costing from a year, it’s a worthwhile upgrade – but one you’ll probably only need if you’re in the wilderness.
One surprising thing we found using the WSD-F21HR when compared to the Garmin Fenix 6X was a noticeable issue with GPS location. It wasn’t massive by any stretch, but we could clearly see a deviation of a few meters across a number of outdoor runs and hikes.
Casio Pro Trek Smart WSD-F21HR: Heart rate tracking features
In terms of sensors, you're getting a fair amount here. Along with built-in GPS, you're also getting a compass (magnetic), pressure (air pressure, altitude) and gyrometer sensors.
Data for most of these sensors is easily accessible through the Tool app. That array of sensors is also now joined by a heart rate monitor.
It was never going to be easy to join the HR party so late in the day, especially when the likes of Polar, Garmin and Suunto are already offering more advanced uses of that heart rate data that go beyond training in heart rate zones.
The F21HR essentially comes with seven activities you can track from the watch: running, trail running, hiking, fishing, snow, trekking, cycling and paddle boarding.
Outside of those options you’ll need to either use Google Fit or download a third party app to track your workouts. There’s no way to include custom or additional activity types using the in-built options.
There are two ways to monitor your heart rate using the watch, the first is to choose the heart rate watch face. Once this is selected, the watch will operate with a primary focus on your heart rate and exercise.
This static screen displays your daily activity. Around the outside is a little graph, which shows peaks over the last 24 hours, the heart in the middle denotes high and low heart rate values for the day, and then there’s also calories burned.
The second screen is the active heart rate display. The main difference here is the live heart rate and the graph on the side, which shows you your heart rate zone.
As far as heart rate tracking goes, there’s nothing particularly groundbreaking here. Those zones are based on a manual resting heart rate you enter at set-up and denote the level of effort your heart is putting in.
If you’re not moving around, the watch will remain on the static screen. As soon as it thinks you’re up and about it’ll turn into the active screen and start tracking your heart rate. If you want to track your heart rate at rest, you’ll have to press the screen to take a reading. The screens can also be slightly modified depending on preference.
The other way to use the heart rate function is to simply start an activity that will prompt the heart rate sensor into action. If you’re looking for rich heart rate-based analytics here, don’t get too excited.
The information you’ll get from the watch is limited to VO2 Max in your post-workout report. It's useful information, but it's nowhere near as comprehensive or detailed as you'd find on a similarly priced sports watch.
Casio Pro Trek Smart WSD-F21HR: Heart rate accuracy
So how accurate is the heart rate monitor on the F21HR? We used it for a variety of activities, specifically focused on running and gym workouts. For running, we downloaded the Strava app and set it up to upload directly, for workouts we used Google Fit – due to a lack of workout support in the watch itself.
When compared with a Polar chest strap and the heart rate monitor on the Garmin Fenix 6X, the heart rate data that we saw was actually fairly consistent with that on the other two devices when looking at the final report, apart from the first few minutes where the Casio seemed to spike incorrectly.
Heart rate accuracy compared: Casio (left), Polar H10 (centre) and Fenix 6X (right)
We did, however, notice on the live readout when training that the numbers seemed to lag, often not coinciding with the level of effort we felt at the time and that had been shown on the Fenix 6X.
When testing the heart rate accuracy against a chest strap (in this case Polar) during interval training the Casio struggled to keep up with the peaks and dips, falling significantly short of the values delivered by the other two devices.
The final averaged HR for that specific workout came in at 105bpm, whilst the chest strap hit 135bpm and the Garmin reported 143bpm.
Unfortunately, it's yet another example of a wrist-based optical heart rate sensor that falters when you are doing high intensity workouts.
Casio Pro Trek Smart WSD-F21HR: The data
As a live data and mapping tool, the WDS F21HR is impressive. For hikers constantly looking at their watch for compass information or to check their elevation it’s an extremely detailed and easy-to-use source of information. That tracked location information can then be used for mapping or to use for future hikes at a later date.
Using the watch as a fitness tracker to store and analyze data is not a user-friendly experience. If you’re tracking your activity from the in-built seven options available, there’s no easy way to access that data once it’s complete.
It’ll give you a final readout of information and then save it as a file in the watch. There’s no app on the watch itself that lets you click through that previous workout data.
Casio has attempted to enable users to access that information by offering integration with Google Drive, exporting workouts and activities as KML or GPX files automatically. It will also update your Google Calendar with the activity. The upshot of that is that you can do what you want with the data from uploading to Strava to using the navigational routes in route-mapping tools.
You can export an overview of your workout data as a raw file but that means you’re essentially just reading a one-off receipt of your activity.
The WSD-F21HR does of course use Wear OS, so there are plenty of tools that you can download to customize and improve the tracking capabilities. We used Stava directly from the phone, which essentially just gives you the ability to track a full activity via the watch and have that data sent to your phone.
Casio Pro Trek Smart WSD-F21HR: Battery life
The battery life of Casio's Pro Trek smartwatches has always been a major area of debate for users. When we heard it was throwing a heart rate monitor into the mix, we were intrigued to see how this would affect battery life performance.
In its normal setting being used as a smartwatch, we found the battery lasted around one and a half days. That’s without taking consistent readings for heart rate or using the GPS, but still being paired to your phone.
While tracking an activity, we found the battery lasted about 15 hours. Not bad for most users, but a definite issue if you’re expecting to head out on an expedition. To rectify this, Casio has implemented a Multi-Timepiece mode, which reverts to the monochrome screen to save battery.
This feature turns off the bulk of the functions that exist, essentially converting it into a run of the mill digital watch with step count or a slightly more functional outdoor option, which includes limited sensor data. This will give you 30 days of battery life.
The watch generally takes about three hours to charge fully, so if you’re on a multi-day hike you’ll need to account for this. As we mentioned previously it also has perhaps the worst charger of any watch currently available. A magnetic rod sticks to the charging opening in the top left of the watch bezel. The slightest knock and it comes out, leaving you with zero charge. It's not the best setup that's for sure.
How we test