So what exactly are those four thingies?

[profmjh]

On the back of the watch, what exactly are those four thingies. Are they all just to measure heart-rate?

 

[nwlondonlad]

They are the sensors that will monitor heartbeat and other functions

 

[troop231]

Two are IR LEDs, and the other two are the actual optical sensors.

 

[profmjh]

They are the sensors that will monitor heartbeat and other functions

What other functions?

 

[nwlondonlad]

Movement via accelerometer and possibly gyroscope.

 

[omgitscro]

Movement via accelerometer and possibly gyroscope.

Accelerometers and gyroscopes are teeny-tiny components mounted on the PCB. What do the LEDs and light sensors have to do with this?

 

[Lennyvalentin]

Two are IR LEDs, and the other two are the actual optical sensors.

Each sensor window contains one set of LEDs and photodiodes; a pair of sensors use green visible light LEDs with matching photodiodes, the other pair uses infra-red LEDs.

Your skin and flesh is too opaque for light from one sensor window to make it to another. These are extremely faint LEDs; a stamp-sized battery runs the entire watch in fitness mode for over six hours.

 

[Mascots]

What other functions?

While HR reading is the primary usage of that sensor, it has a few other use cases.

For example, the sensor is responsible for determining if the Watch is in use to prevent notifications from firing when it's not on you.

But as far as any extended functionality, that's about it. Just use cases for a sensor that acknowledges your presence and gives metrics on your heart.

 

[nwlondonlad]

Accelerometers and gyroscopes are teeny-tiny components mounted on the PCB. What do the LEDs and light sensors have to do with this?

Everything and nothing

 

[Appl3FTW]

ET go home lights