Shoulder surfing is a technique criminals use. The criminal will stand very closely behind or near someone in an attempt at seeing their phone or ATM pin as it is entered. This also works with laptops, pin-unlock doors, and other similar devices. Researchers from the NYU Tandon School of Engineering have invented a new technology called IllusionPIN that thwarts shoulder surfing.
IllusionPIN is a virtual keyboard like the one that pops up on mobile phones or is used by touchscreen kiosks. At close range it works normally, but at a distance of three feet or more it looks completely different. The person using the device sees one input screen, and the person shoulder surfing sees a completely different input screen. They achieve this effect using two different frequencies in the same image. One person sees the low frequency image and another sees the high frequency image. The distance you are from the image determines which image your eyes will see.
In testing the IllusionPIN system thwarted shoulder surfing 21 out of 21 times. In the control group without this technology the shoulder surfer was successful all 21 times. Hopefully this catches on. It would be a great feature for bank ATMs!