Researchers at the University of Massachusetts Lowell found that by using wearable devices like Google Glass, they were able to identify four-digit passcodes people tapped into a tablet by studying the movement of the victim’s finger from a distance of 10 feet.

With a high-definition video camera, the same effect was replicated at 150 feet. The researchers were able to achieve 90 percent accuracy with their Google Glass tests. The team used software that mapped the images collected by their cameras and translated the shapes and movements of the finger shadows into passcodes.