CorSense Reading Before Finger is Inserted
Whenever the CorSense is activated through movement, it starts looking for a Bluetooth connection. Once you connect to it, then it starts looking for a pulse.
Certain light patterns can match patterns that you'd expect to see in a pulse, so the unit may temporarily be tricked into thinking it sees a pulse if all of the aforementioned steps are fulfilled.
Once you stick your finger in, the Corsense doesn't have any problem differentiating your pulse from other light patterns, and the shape and form of the device are set up to prevent issues with that anyway.
In the absence of a finger, the sensor window is exposed and could detect light patterns similar to a pulse from time to time. Again, it would only be if an app or software was connected and telling it to sample for data.
Make sure your finger is inserted before you exit the Live Preview period, so all data collected during the reading is yours.