How to Track Heart Rate Accurately With a Budget Smartwatch

Heart rate monitoring is one of the most-used features on any smartwatch, yet it is also one of the most misunderstood. If you have ever glanced at your wrist mid-workout and wondered whether those numbers are actually accurate, or found your resting heart rate reading wildly different from what your GP measured, you are not alone. Getting accurate, reliable heart rate data from a budget smartwatch is absolutely achievable, it just requires understanding how the technology works and a few simple habits that genuinely improve measurement quality.

How Do Smartwatches Actually Measure Heart Rate?

Almost every consumer smartwatch on the market today, including the entire COLMI range, uses a technology called photoplethysmography, or PPG. It sounds complicated, but the principle is elegantly simple. The green LED lights on the underside of the watch shine into your skin. Blood in your capillaries absorbs green light more effectively than surrounding tissue, and crucially, the amount it absorbs changes with each heartbeat. When your heart contracts and pushes a pulse of blood through your vessels, more blood is present, and more light is absorbed. Between beats, less blood is present and less light is absorbed.

The photodetector next to the LEDs measures these tiny fluctuations in how much light bounces back to the sensor hundreds of times per second. By analysing the pattern of these fluctuations, the watch processor calculates your heart rate with remarkable accuracy, when conditions are right.

Why Are Readings Sometimes Inaccurate?

Understanding the conditions that affect accuracy is the key to getting better data. Here are the most common causes of inaccurate smartwatch heart rate readings.

1. Watch Position on the Wrist

This is the single most common cause of inaccurate readings, and the good news is it is entirely within your control. Most people wear their watch too loosely or too low on the wrist, particularly after a few hours when the watch has naturally slipped down toward the wrist bone. For accurate readings, the watch should sit one to two finger-widths above your wrist bone, with the sensor making firm but comfortable contact with your skin. You should be able to slip one finger underneath the strap, but not two.

2. Movement and Motion Artefacts

During high-intensity exercise, particularly activities involving vigorous wrist movement like boxing, kettlebell training, or rowing, the sensor can struggle to distinguish your actual pulse from the noise generated by physical movement. This interference is called motion artefact and it is an inherent limitation of optical wrist-based sensors generally, not a specific flaw of any one device.

3. Cold Temperatures

When you are cold, your body's natural response is to restrict blood flow near the skin surface, a process called vasoconstriction, to conserve core body heat. Less blood near the surface means less signal for the sensor to detect, resulting in less accurate readings until your body warms up.

4. Skin Tone and Melanin

Green light is absorbed more by melanin, the pigment that gives skin its colour, as well as by blood. This means that on darker skin tones, the sensor has to work harder to separate the signal from the noise. While most modern sensors are calibrated to compensate for this, some level of reduced accuracy can still occur.

5. Tattoos

Tattoo ink, particularly dark colours like black, blue, and green, absorbs the LED light in a similar way to blood, which can confuse the sensor and produce inaccurate readings. If you have tattoos on your wrist, the watch may work better worn on the other wrist, or positioned higher on the forearm.

6. Skin Condition and Dryness

Very dry skin, calluses, or skin conditions can affect how light penetrates into the tissue and reflects back to the sensor. Keeping the skin under the watch clean and reasonably moisturised can help maintain consistent sensor contact quality over time.

Practical Tips for More Accurate Readings

For Resting Heart Rate

• Take resting readings first thing in the morning, before getting out of bed or having caffeine
• Sit still for at least 5 minutes before initiating an on-demand measurement during the day
• Make sure the watch fits snugly, the sensor must maintain consistent contact
• Avoid caffeine or strenuous activity in the hour before a resting reading you want to rely on

During Exercise

• Slide the watch slightly higher up your wrist before starting exercise, this can significantly improve accuracy during movement
• Enable continuous heart rate monitoring mode before your workout rather than relying on on-demand readings during exercise
• For very high-intensity exercise, consider using the watch data for general trends rather than exact numbers
• If you are sweating heavily, wipe the watch and your wrist during breaks to ensure good sensor contact

General Daily Use

• Clean the back of the watch regularly with a soft, slightly damp cloth, sweat, skin oils, and dust can build up on the sensor
• Let the watch settle on your wrist for 30 to 60 seconds after putting it on before taking any health readings
• Use the trend data in your companion app, DaFit, rather than individual readings for the most meaningful health insights

What Is a Normal Resting Heart Rate?

For most healthy adults, a normal resting heart rate falls between 60 and 100 beats per minute, bpm. Where you fall within that range depends on your age, fitness level, and individual physiology: 60 to 75 bpm is good for most adults, 50 to 65 bpm is typical for regularly active individuals, 40 to 55 bpm is common in endurance athletes, this is healthy, not cause for concern, and above 90 to 100 bpm consistently is worth discussing with a doctor if there is no obvious cause.

How Accurate Are Budget Smartwatches Compared to Medical Devices?

Consumer smartwatches are not medical-grade instruments. Compared to an electrocardiogram or clinical pulse oximeter, they have higher margins of error. Multiple studies have shown that optical wrist-based sensors typically achieve accuracy within 3 to 5 bpm of a chest strap during moderate activity, with accuracy declining during high-intensity exercise. For resting measurements, accuracy is generally better, often within 2 to 3 bpm of a clinical reading, more than sufficient for fitness and wellness monitoring purposes.

Which COLMI Watches Are Best for Heart Rate Monitoring?

All COLMI smartwatches include optical heart rate sensors, but some have enhanced sensor setups. The COLMI i28 Ultra uses a dedicated LC09A heart rate sensor chip alongside the main processor, providing improved accuracy across a range of conditions. The COLMI V72 also incorporates the LC09A chip. The COLMI V75 GPS combines continuous heart rate monitoring with built-in GPS, ideal for runners correlating heart rate with pace and route.

If heart rate accuracy during sleep is your priority, consider pairing your smartwatch with a COLMI smart ring, the finger-based sensor placement typically produces more reliable overnight readings than a wrist-based watch.

Should You Trust Smartwatch Heart Rate for Medical Purposes?

Use it as a valuable and informative guide, not as a medical device. Consumer smartwatches are excellent for spotting trends and providing general wellness insights, but not appropriate for diagnosing heart conditions or guiding treatment decisions. If you have a diagnosed heart condition, always use devices recommended by your doctor.

Final Thoughts

Getting accurate heart rate data from your COLMI smartwatch is very achievable with the right habits. Wear it correctly, keep it clean, take resting readings under consistent conditions, and focus on trends rather than individual readings. Over time, the data your watch collects will give you genuinely useful insights into your cardiovascular health, recovery, and fitness progress.

Ready to start tracking? Explore the full COLMI smartwatch range and find the right health monitoring companion for your lifestyle.