The Green Laser
The Apple Watch is famous for its fitness tracking, powered by an optical Heart Rate sensor on the back of the device. This sensor uses bright green LED lights that flash against your skin hundreds of times a day to calculate your pulse in the background. While useful for health analytics, this sensor is one of the heaviest battery drains on the device. Furthermore, if you wear your watch slightly loose in a dark room, the bright green flashing light can be incredibly distracting. If you only use your Apple Watch for notifications and telling time, and you have no interest in fitness tracking, you must permanently kill this sensor.
How to Turn Off the Heart Rate Sensor
You can permanently sever power to the optical LEDs 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).
Massive Battery Savings
The change is instantaneous. The Apple Watch will completely cut the electrical feed to the optical sensors on the ceramic backplate. The green LEDs will instantly shut off and will never again randomly flash against your wrist. The watch will instantly stop generating background health data, and because the device is no longer constantly pulsing a bright light into your skin, you will immediately notice a significant increase in your daily battery life.