You may see green and red lights flashing on the back of your Fitbit. This is normal, but understanding what they are can be helpful.
Let's See What Are They?
Green light flashing on the back of your Fitbit usually indicates the device is continuously monitoring your heart rate.
The amount of blood in your wrist increases and decreases as your heart beats.
Your Fitbit calculates the number of heartbeats per minute from the rise and fall of the absorption signal.
On the other hand, the red light on Fitbit is used to determine your oxygen levels by using a method called Pulse Oximetry.
Turning off Heart Rate feature on your Fitbit stops the green light from flashing. Likewise, if you disable SpO2 monitoring, the red light goes off.
To turn off the flashing Green light, Go to Settings > Heart Rate > Disable.
However, turning off SpO2 is not an available option on Fitbit yet.