In order to use the Thumb Sensor on your emWave2 device, start the emWave2 and put your thumb on the sensor - LIGHTLY but completely.
In order for the thumb sensor to operate correctly, it is important to hold the emWave device correctly. Do this in the direction of the indentation on the device. Hold the unit like you would a playing card with your thumb running vertically over the sensor. The ear sensor and charging ports, on the bottom of the unit, should be in the web of your thumb. It doesn't matter which hand you hold the emWave device in, the lights will be to the left of your thumb.
NOTE: Pressing too hard on the sensor causes the sensor to be more of a button than a sensor and can cause the other modes to be activated. All of the additional functions of the emWave2 device are located in the multi-function sensor / button.