Although the emWave 2 comes with an ear sensor....if you need an extra emWave Ear Sensor for emWave Pro, EmWave 2 or Inner Balance technologies you can order separately. A USB Module is required for use with emWavePro. The emWave Ear Sensor has excellent signal quality and is comfortable for extended wear plus fits all sizes (child to adult). All emWave and Inner Balance products already come with an ear sensor but if you need an extra one or lose yours, we keep these in stock.