(Please Note: This solution will work on Yosemite to current OSX.)
Sometimes after upgrading your Mac OS, the emWave2 and emWave Pro programs are unable to find the Sensor/Devices.
Try this first:
Quit the emWave application.
Go to Library / Application Support / emWave To find it, double click on the Yosemite hard drive icon or find the Macintosh HD. Select Library, then select Application Support.
Delete the emWave folder you see in the Application Support folder.
Run the application, it will reinstall Application Support files automatically. Try running a Session again. If you are still having difficulties, please contact HeartMath Tech Support: [email protected]