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How to get more accurate wrist heart rate readings – tips and troubleshooting steps

Getting started

Wrist heart rate (WHR) technology measures heart rate via LEDs that track blood flow in your wrist. This means that you can see your heart rate data during your exercise or in daily use without a chest heart rate strap. The wrist HR technology in the following Suunto watches is provided by Valencell Inc.: Suunto 9 Baro, Suunto 9, Suunto 5, Suunto 3, Suunto 3 Fitness, Suunto Spartan Sport Wrist HR Baro, Suunto Spartan Trainer Wrist HR, Suunto Spartan Sport Wrist HR.

The accuracy of optical HR measurement is influenced by a number of factors and can be affected by individual differences between people. Therefore, wrist heart rate measurement should be considered an estimate. For more accurate readings, we recommend using a compatible chest heart rate sensor such as the Suunto Smart Heart Rate Belt and Smart Sensor.

How to wear your Suunto wrist heart rate monitor watch - better fit for better readings 

One of the factors with the biggest impact is how you wear your wrist heart rate tracker. The right fit can help improve the accuracy of your heart rate readings. Start with the following tips, and then test and improve the fit of your watch until you find your personal sweet spot.


During daily use

Wear your Suunto watch at least 1 finger above your wrist bone and make sure the watch is snug on your wrist. Your watch should always maintain a contact with your skin, so that you can't see the light shining from the sensor.


During exercise

Test the fit – the key is to wear the watch as high up on your wrist as possible, and to prevent it from sliding down during exercise. A good indicator is to wear it about 2 fingers above your wrist bone. Again, make sure you wear the watch tight and evenly against the skin, however not too tight to cut off blood circulation.


Too loose

 Just right


Keep in mind when wearing a wrist HR tracker

For best possible results:

  • Warm-up to get your heart rate up before starting your training. This ensures your watch provides stable readings from the start.
  • If your watch loses your heart rate during exercise, pause for a moment (approximately 10 – 30 seconds). Continue once your watch is locked onto your heart rate.

Try to avoid:

  • Wearing the watch too loose. Make sure the sensor is always in direct contact with your skin: you shouldn't be able to see the light shining from the sensor.
  • Wearing the watch too tight. Wearing the watch extremely tight can cut off blood flow and reduces the sensor's ability to monitor heart rate.

Keep your skin happy:

  • Regularly take the watch off your wrist, wash the watch and the strap with mild hand soap and water, rinse thoroughly and dry it well with a towel before putting it back on.
  • We recommend washing the watch body and the strap after every heavy workout.
  • To remove build-up of lotions and oils (such as sunscreen, insect repellent and moisturizers) that can be trapped beneath the strap: use mild hand soap, rinse thoroughly and dry well with a towel.
  • Wearing your watch long-term on the same wrist may irritate your skin. Let your skin rest on a regular basis, by taking your watch off or switching the watch to the other wrist.
  • Please note: allergenic substances like fruit juice, raw potato, celery, albumen, corn, beans, peas, seafood, nuts, soy, wool etc., and abrasive substances like dust, sand and some skin lotions trapped under strap may cause severe skin irritation very quickly.

Learn more about how to care for your Suunto watch and skin

How optical heart rate measurement works

In practice, the optical heart rate sensor on the underside of the watch shines light into your wrist using LEDs and measures the light that is scattered by blood flow. This is based on the fact that light entering the body will scatter in a predictable manner when the blood flow dynamics change, such as with changes in blood pulse rate or with changes in blood volume (cardiac output).

Good to know about wrist heart rate measurement

Wrist heart rate measurement is an easy and convenient way to track your heart rate. However, please keep in mind that the accuracy and reliability of optical heart rate measurement varies from person to person and may not work at all with certain types of activities or sports. Currently, the best wrist heart rate measurements stay 90% of the time within 5% of the chest-measured heart rate.

Together with Valencell, we identified the following factors that may affect heart rate measurement:

  • When exercising in cool or cold temperatures, your body attempts to keep your body temperature stable by directing the blood flow from arms and legs towards the core of your body. This reduction in blood flow to the arms can make it more difficult for the sensor to measure heart rate accurately.
  • If you frequently have cold hands, a proper warmup before exercising may be needed to improve the accuracy of heart rate readings.
  • Arm movements and flexing muscles, such as gripping a tennis racket or doing Crossfit style high-intensity training, and sports involving strong vibration as e.g. when cycling on uneven, bumpy terrain, can change the accuracy of the sensor readings.
  • The heart rate sensor may not provide accurate heart rate readings for swimming activities, as water passing under the watch affects the optical sensor's ability to read heart rate accurately.
  • Dark tattoos can prevent reliable readings from the optical sensor.


Troubleshooting tips: 

Update the software of your product

One of the most important ways to get the best wrist HR performance is to ensure your watch is on the latest software version. We continuously improve the software of our products and make performance enhancements and fix bugs that we see in the field. Learn more about software updates for your product and how to install the software on your watch.

No wrist heart rate data is recorded

During daily use: If your heart rate sensor failed (not detecting / reading your heart rate), and if the heart rate sensor lights at the back of the watch are not blinking (wrist heart rate sensor seems to be not working / turned off), check that Daily HR is activated. Open Settings > Activity > Daily HR and ensure that the toggle is green. This ensures continuous heart rate tracking during daily use.

During exercise: If the wrist heart rate sensor seems to be not working before starting an exercise, ensure that your watch is not paired with a HR belt. Open Settings > Connectivity > Paired devices. If HR sensor is listed, press the middle button and forget.

If the mentioned tips did not solve the issue, or if your watch is not picking up your pulse or if the sensor is otherwise malfunctioning, a soft reset may solve the issue. Learn how to reset your watch

Too high or low heart rate readings at exercise start

If your watch shows inaccurate heart rate readings at the start of your exercises, a warm up may solve the issue:

  • Warm up for yourself: The quality of wrist-based HR measurement heavily depends on the blood flow to your arms and hands. A proper warm up for 10-15 minutes increases the blood flow and improves the quality of WHR readings.
  • Warm up for the heart rate sensor: The sensor needs some time (several minutes) to lock on your heart rate. To give the sensor time to warm up, we recommend opening the exercise start screen already while getting ready for your workout (e.g. when changing clothes).



More accurate readings with a chest heart rate sensor

For more accurate readings in all circumstances, we recommend using a compatible chest heart rate sensor such as the Suunto Smart Heart Rate Belt. Using a heart rate belt will enable getting heart rate readings also when mounting the watch on the handlebar of a bike or wearing it on top of a sleeve.

When having a heart rate belt paired with your watch, the heart rate icon on the exercise start screen will include a small belt. When using wrist heart rate, the icon will be in heart shape only.





Always remember that heart rate readings, optical or otherwise, are estimates and only for reference and recreational use and not intended for medical use of any kind.

If you have tried all mentioned tips and troubleshooting steps, but the issues with your Suunto device persist, please contact our Suunto Support. We are happy to assist you.