In a research performed at UCSD that involved 21 volunteers who punched in 27 randomly selected PIN numbers on both plastic and brushed metal keys, plastic PIN pads can retain the heat signature from the finger for the longest – which in turn, reveals the order they were pressed.
Of course, there are other variables to be taken into consideration – including how hard you press the buttons, while your body temperature can also affect the results. Metal PIN pads work better in your favor as a withdrawee since they do not retain heat long enough to show just which keys were pressed. The software that analyzes these heat signatures can determine the PIN number 80% of the time within 10 seconds, and when 45 seconds has passed, the success rate remains at 60%. Best to wear gloves the next time round, no?