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Heart rate sensors measure your pulse two ways: optical PPG sensors shining light into skin, or ECG sensors reading the heart’s electrical signal.
For the full breakdown, see our best Wireless Heart Rate Sensor guide.
Every time a smartwatch or fitness tracker shows your beats per minute, a sensor on your wrist just measured something real about your body. Understanding how a heart rate sensor works comes down to one idea: the device detects a physical signal your heart produces with every beat, then turns that signal into beats per minute (bpm).
Two Technologies, One Number: PPG vs ECG
Heart rate sensors fall into two technology families. Optical PPG (photoplethysmography) sensors measure blood-volume changes in your tissue with light. ECG (electrocardiogram) sensors measure the heart’s electrical signals directly through electrodes.
ECG is the medical-grade method. It reads the electrical activity that makes the heart muscle contract, and it’s built into certain