What does the ear clip monitor?

The forehead sensor detects electrical signals from the brain. At the same time, the sensor also picks up ambient noise from the body (generated by muscle movement), and other electrical devices like computers, light bulbs, and electrical sockets. The ear clip acts as a ground and reference, which allows NeuroSky’s chip to filter out all of the electrical noise from the body and the ambient environment, and hone in on brainwaves.