If you’re looking for a simple way to increase the security of PIN passcodes on devices with touch screens you can do so by repeating a digit in the sequence.
Over at Tech Crunch they highlight a downside to touchscreen PIN interfaces and a way you can easily improve security. First the problem: if you use a four digit PIN with four unique numbers, your finger prints give you away. The marks left on the screen identify the buttons pressed and reduce the high number of combinations yielded from a 4 digit pin (10,000) to a very low number of combinations one can create with only 4 numbers (24).
The solution? By simply doubling up one of the digits (i.e. using the number 5 twice in the sequence like 5785) you increase the potential variants to 36. It’s a marginal increase to be sure but it introduces an additional challenge to someone snooping on your phone with absolute zero effort on your part.
Want to Make Your iPHone’s PIN More Secure? Repeat a Digit. [Tech Crunch]