To see the virtual environment in stereoscopic 3D, users wear liquid crystal shutter glasses (usually, Stereographics' CrystalEyes). These glasses are very fragile. These glasses will usually have an on / off switch to keep the batteries from draining when not in use. The glasses need to be turned on in order to see in stereo. Failing to turn the glasses on is a common error for new users. Anytime demos are given more experienced users should make sure any new users are indeed seeing in stereo. The glasses will not work if the user is facing away from the emitters, and will turn off when not receiving the IR signal.