What’s the two red squares on the top and bottom on the back of the Fitbit Inspire 2?

[ahawkua]

What’s the two red squares on the top and bottom on the back of the Fitbit Inspire 2? I know the middle green one is the heart rate sensor. Are all three LEDs?

This is what I’m talking about 

[LZeeW · Accepted solution]

@ahawkua   The heart rate sensor has two parts, an emitter and a sensor.  The Inspire 2 has one emitter, the green LED that shines the light.  Those red squares are the sensors, not LEDs.  They gather the reflected light.  Different models have different combinations of emitters/sensors.  I still have an old Charge 2 in a box.  It has two emitters and one sensor.

[ahawkua]

Is there official Fitbit documentation saying the spo2 sensor is an LED?

[LZeeW]

@ahawkua   To clarify things, the Inspire 2 doesn't measure SpO2.

[Rich_Laue]

For oxygen sensing, a red and infrared led is needed. 

Yes they are simple LEDs and not a laser led which would quickly burn the skin.