The differences between ECG heart rate monitors and optical heart rate monitors - Coolblue - anything for a smile
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Amazon.com: 2023 Upgrade 2.0" with the Smart Watch (Answer/Make Call), Smartwatch for Women Men, Fitness Tracker with Multi Sport Modes, IP68 Waterproof, Step Calorie Counter, Sleep/Heart Rate Monitoring Watches : Electronics
What does heart rate monitor do & how does it work on smart watch?