The infrared camera shows a thermal signature left by your fingers when you type codes at ATM keypads, door entries and more. All a thief has to do is scan their camera right after you enter the code to see which keys have recently been used. Since the heat signature fades with time, you can even see the order which the keys were pressed. The 'hotter' keys were likely pressed last while the 'dimmer' keys were likely pressed first.
A study at UC San Diego shows that it is possible to guess the correct code 80% of the time if the image was taken immediately after. If the image was taken 1 minute later, there still was a 50/50 change of guessing the correct code.
However, this trick won't work on keypads such as metal ones, which reflect IR. To prevent this trick, Rober recommends you rest your fingers over other buttons while entering your real pin or passcode.
Infrared cameras have been around for a while, but recent accessories like the FLIR ONE bring the device at a reasonable cost to the iPhone.
For more videos like this, please follow iClarified on Twitter, Facebook, Google+, or RSS.