The Polar H10 sensor is placed on the body.

Connect your Polar H10 to Galaxy watch 4/5. This is how one can do using Google Fit & sync it to Samsung Health. : r/GalaxyWatch

Heart rate monitoring of the endurance runner during high intensity interval training: Influence of device used on training functions - Santiago A Ruiz-Alias, Felipe García-Pinillos, Víctor M Soto-Hermoso, Emilio J Ruiz-Malagón, 2023

The Polar H10 sensor is placed on the body.

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Wireless heart rate monitoring technology and motion capturing