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Suunto 9 Peak Pro User Guide

Optical heart rate

Optical heart rate measurement from the wrist is an easy and convenient way to track your heart rate. Best results for heart rate measurement may be affected by the following factors:

  • The watch must be worn directly against your skin. No clothing, however thin, can be between the sensor and your skin.
  • The watch may need to be higher on your arm than where watches are normally worn. The sensor reads blood flow through tissue. The more tissue it can read, the better.
  • Arm movements and flexing muscles, such as gripping a tennis racket, can change the accuracy of the sensor readings.
  • When your heart rate is low, the sensor may not be able to provide stable readings. A short warm up of a few minutes before you start the recording helps.
  • Skin pigmentation and tattoos block light and prevent reliable readings from the optical sensor.
  • The optical sensor may not provide accurate heart rate readings for swimming activities.
  • For higher accuracy and quicker responses to changes in your heart rate, we recommend using a compatible chest heart rate sensor such as Suunto Smart Sensor.

The optical heart rate feature may not be accurate for every user during every activity. Optical heart rate may also be affected by an individual’s unique anatomy and skin pigmentation. Your actual heart rate may be higher or lower than the optical sensor reading.


Only for recreational use; the optical heart rate feature is not for medical use.


Always consult a doctor before beginning a training program. Overexertion may cause serious injury.


Allergic reaction or skin irritations may occur when products are in contact with skin, even though our products comply with industry standards. In such event, stop use immediately and consult a doctor.

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