The Battery Drain
The Apple Watch utilizes a green LED optical heart sensor on its ceramic back to constantly monitor your pulse. By default, even when you are not actively working out, the watch wakes this sensor up in the background throughout the day to calculate your resting heart rate and monitor for irregular rhythms. While this provides excellent long-term health data, these constant background optical scans are one of the heaviest drains on the device’s battery. If you only care about heart rate during active, manually triggered workouts, you must disable the background scanning daemon.
How to Turn Off Background Heart Rate Measurements
You can permanently paralyze the passive optical sensor via the Privacy settings.
- Open the Settings app directly on your Apple Watch (the grey gear icon).
- Scroll down the main list and tap on Privacy & Security.
- Tap on Health.
- Tap on Heart Rate.
- Locate the master toggle switch labeled Heart Rate.
- Toggle this switch to the Off position (the green background will disappear).
Manual Tracking Only
The change is instantaneous. The Apple Watch will completely terminate the background daemon responsible for randomly firing the green LEDs throughout the day. The watch will absolutely refuse to passively track your resting heart rate, your walking average, or alert you to irregular rhythms. However, the hardware is not permanently disabled. If you manually open the Workout app and start a run, the sensor will still activate and track your pulse during the exercise, guaranteeing maximum battery life while retaining active fitness capabilities.