If you follow my training journey, you know I’m meticulous about tracking data. Whether I'm out for an early morning run or spinning on the trainer, having an accurate heart rate reading is non-negotiable. I recently dropped by the Decathlon Sri Damansara branch and picked up the Decathlon HRM Armband (Brassard)for RM149.

At this price point, it’s positioned right in the sweet spot for runners and triathletes looking to ditch the restrictive chest strap without breaking the bank. Some say it's an OEM version of the Magene H03, but for RM149 with a 2-year Decathlon warranty, it's an absolute no-brainer on paper.

Here is my breakdown of how it holds up in real-world use.

The Unboxing & Build

The package is about as minimalist as it gets. Inside the box, you get the sensor unit, the 26mm Velcro armband, a magnetic charging cable, and the standard manual/warranty booklet.

The unit itself is incredibly light, weighing in at just 21 grams. The strap is soft and elastic enough that you easily forget it's there once it's tensioned on your forearm or bicep.

One minor caveat: The 26mm strap isn't sold as a standalone spare part by Decathlon Malaysia just yet. If you wear it out over months of sweaty mileage, you will have to scour third-party online platforms to find a generic replacement.

Operation & Ecosystem Connectivity

Simplicity is the theme here. There is only a single physical button on the face of the unit.

Powering On: A single quick press turns it on, flashing a blue light as it begins searching for a signal. It features dual-protocol ANT+ and Bluetooth Smart connectivity, making it universally friendly.

Pairing: It paired instantly as an external sensor with my Garmin Forerunner 965 and my Edge 1040 Solar. If you run older ecosystems from Coros or Suunto that rely heavily on ANT+, it should connect without a hitch, though it’s always wise to double-check your device's specific specs. Once paired, the blue indicator light switches off so it isn't distracting you during night runs.
Powering Off: Hold the button down for 3 seconds. It will blink to indicate battery status before shutting down—a green flash means you are sitting safely above 20% battery life.

Performance & Battery Life

The optical sensor placement on the arm inherently solves a lot of the standard cadence-lock issues you get with wrist-based optical sensors on GPS watches. During steady-state runs and aerobic base training, the readings remained highly stable, matching closely with what I typically expect from high-end dedicated units.

Battery life is stellar for a device this compact. Decathlon claims a 30-hour autonomy on a single charge. Charging from empty back to full takes just about 1 hour via the included magnetic puck. Not having to swap out CR2032 coin cells every few months is a massive quality-of-life win.

Real Life Test

Wrist HR vs Optical Armband HR: Does Sensor Position Really Matter?

Heart-rate data has become almost invisible in endurance training. Start the watch, start running, and a few seconds later there’s a number telling you how hard you’re working.

But how much should we actually trust it?

I recently compared wrist-based optical heart rate against an optical HR armband during training. Both use essentially the same underlying technology, photoplethysmography or PPG, which detects changes in blood volume beneath the skin. The big difference is where the measurement is taken.

And that seemingly small change in location can make a surprisingly noticeable difference.

Wrist HR vs Arm HR: Same Technology, Different Location

A modern sports watch shines light into the skin at the wrist and uses the reflected signal to estimate each heartbeat.

An optical armband works on the same principle, but places the sensor higher up the arm or forearm.

That potentially gives the armband an advantage.

The wrist is constantly moving during running. Watch movement against the skin and changes in contact between the optical sensor and wrist can interfere with PPG measurements.

Research has nevertheless shown that wrist optical HR can perform quite well during relatively steady walking and running. One study involving 50 participants found mean absolute percentage errors of roughly 3.3% to 6.2% across six optical HR devices compared with a Polar chest strap. [pmc.ncbi.nlm.nih.gov]

The problem becomes more apparent as exercise and movement become more demanding.

A 2025 study comparing a wrist-worn Fitbit Charge 5 against the Polar H10 found that measurement error could increase at higher exercise intensities, with the magnitude of error also differing across skin tones.

Rather than simply comparing the final average HR, I would pay particular attention to the HR trace over time.

Two sensors could both produce, say, an average of 148 bpm, while behaving very differently during the workout.

If the actual HR rises:

140 → 150 → 160 → 170 bpm

but one device responds:

140 → 143 → 152 → 164 bpm

the final averages might look reasonably close, yet one sensor isn't necessarily giving you the same information when you need it.

That's particularly important for intervals.

Why I Prefer the Armband for Training

Interestingly, newer research directly investigating anatomical placement supports the idea that where an optical sensor sits matters.

A study comparing the Polar Verity Sense on the forearm, a Garmin Forerunner at the wrist and multiple WHOOP 4.0 sensors at different arm positions against a Polar H10 found accuracy was excellent at rest but generally declined as movement intensity increased. [mdpi.com]

That's why an optical armband represents an interesting middle ground for endurance athletes.

	Wrist optical	Optical armband
Convenience	★★★★★	★★★★☆
24/7 monitoring	★★★★★	★★☆☆☆
Steady running	Good	Very good
Rapid HR changes	More challenging	Generally better positioned
Cycling	Can be affected by wrist position	More isolated from wrist movement
Comfort	Nothing extra to wear	More comfortable than a chest strap for some
Training HR	Good for many sessions	My preference if HR matters

But What About a Chest Strap?

If outright HR accuracy is the objective, I'd still consider an ECG-based chest strap such as the Polar H10 the benchmark rather than either optical solution.

That's an important distinction.

This isn't really:

Armband = perfectly accurate

It's more:

Wrist → optical armband → ECG chest strap

as you move from maximum convenience towards a more dedicated HR measurement solution.

For long easy runs and everyday training, wrist HR may be completely adequate.

For a five-hour ride, I'd happily use an optical armband if comfort mattered.

TL;DR - The Final Verdict

The biggest lesson from my comparison isn't that wrist-based HR is bad.

It isn't.

Wrist HR has become good enough that for a huge percentage of my training, I could simply wear the watch and forget about it. Previous validation research has found surprisingly good performance from several wrist/arm optical devices during continuous walking and running. [pmc.ncbi.nlm.nih.gov]

But "good enough" and "the measurement I want to base my training on" aren't quite the same thing.

For me, an optical armband occupies a sweet spot.

Watch only: everyday training and convenience.

Optical armband: when I care about HR data but don't want a chest strap.

Chest strap: intervals, threshold testing and sessions where HR accuracy really matters.

And perhaps that's the better way to look at heart-rate sensors.

Don't ask which one is best?

Ask:

How accurate does this particular workout need to be?

That determines what I put on before pressing Start.

If you are looking for an affordable, comfortable, and reliable heart rate monitor to offload tracking from your wrist—or if you absolutely despise the tight squeeze of a chest strap—the Decathlon HRM Armband fits beautifully into your gear rotation.

It provides seamless connectivity, excellent battery life, and the peace of mind that comes with Decathlon’s solid local warranty. For RM149, I have absolutely no complaints.

Personal thoughts: It's an easy "yes" for any multi-sport athlete looking for functional utility without the premium price tag.

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