When does ScanWatch measure your heart rate?
When you use the Workout Mode, ScanWatch measures your heart rate continuously during the workout. In addition, ScanWatch measures your heart rate throughout the day when you’re motionless, and periodically when you’re walking. Since ScanWatch takes these background readings based on your activity, the time between these measurements will vary.
How does ScanWatch measure your heart rate?
The optical heart sensor in ScanWatch uses what is known as photoplethysmography (PPG). This technology is based on a very simple fact: Blood is red because it reflects red light and absorbs green light. ScanWatch uses green LED paired with light‑sensitive photodiodes to detect the amount of blood flowing through your wrist at any given moment. When your heart beats, the blood flow in your wrist — and the green light absorption — is greater. Between beats, it’s less. By flashing its LED lights thousands of times per minute, ScanWatch can calculate the number of times the heart beats each minute — your heart rate. The optical heart sensor supports a range of 30–210 beats per minute. In addition, the optical heart sensor is designed to compensate for low signal levels by increasing both LED brightness and sampling rate.
ScanWatch uses green LED lights to measure your heart rate during workouts.
ScanWatch also measures your heart rate when manually recording an electrocardiogram (ECG). It has built-in electrodes in the bezel (the upper ring) and the back, which can measure the electrical signals across your heart when used with the ECG recording. When you place your finger on the bezel, it creates a closed circuit between your heart and both arms, capturing the electrical impulses across your chest.
To use the electrical heart sensor to measure your heart rate, select the ECG mode on the watch and place your finger on the bezel.
- ScanWatch cannot detect heart attacks. If you ever experience chest pain, pressure, tightness, or what you think is a heart attack, call emergency services immediately.
- ScanWatch does not constantly look for AFib. This means ScanWatch cannot detect all instances of AFib, and people with AFib may not get a notification.
- If you’re not feeling well, you should talk to your doctor even if you don’t get a notification. Symptoms such as a rapid, pounding, or fluttering heartbeat, dizziness, or fainting, can indicate a serious condition.
- Do not change your medication without talking to your doctor.
- In some instances, the notification may indicate the presence of an irregular heart rhythm other than AFib.