The Pulse light on the emWave2 is a critical indicator of the unit.
As long as the small blue, Pulse light is blinking, the sensor has acquired your pulse and is interpreting data for the emWave2.
If the little blue light stops blinking, it means that the pulse connection has been lost.
IMPORTANT NOTE: When enough time has passed without the pulse being acquired or the blue light has stopped flashing, the emWave2 will shut itself off in a power saving feature.
If this happens during a session, it may appear to be something else but this is a normal function of the emWave2.