Once the watch and sensor are connected you really don’t need the watch anymore except to monitor the sensor and make sure you are still getting a reading. It is useful to inform the user in case the sensor has shifted or is blocked for some reason. But the sensor will continue to collect data once connected even if the watch loses connection. It is intended to work this way so if the watch connection is lost, you can continue the workout without interruption and look at the data afterwards. Or maybe you prefer not to wear the watch at all during workout because it gets in the way but you want the data.
When you first turn on the sensor, the LED will flash once per second. Once connected, the LED will be on continuously until the sensor is turned off. Data is being collected on the sensor when the LED is on steadily.
Just turning off the watch will not stop the sensor. You need to also turn off the switch on the sensor when done with the workout.
Only valid SmO2 data is stored. If the sensor is off muscle or blocked, data will not be recorded. You will see this when retrieving data and there are gaps. Valid data is stored every two seconds.