Google Cardboard V2.0
Operating Systems: Android 4.1 or higher, or iOS 8.0 or higher.
Screen Sizes: 4 to 6 inches.
Recommendations from Google:
Take frequent breaks while using a VR viewer. If you experience nausea, discomfort, eye strain, or disorientation, immediately discontinue use. Not for use by children without adult supervision. Do not use a VR viewer while driving, walking, or otherwise by being distracted from real world situations that prevent you from obeying traffic or safety laws. Do not drive or operate heavy machinery immediately after using a VR viewer if you feel impaired or disoriented. If you may be prone to seizures, consult a doctor before use.