I think that this is an attempt to stop the “clean key” problem. Security system keypads (especially outdoor ones) tend not to be cleaned, so as time passes, it is easy to spot the dirty keys. Dirty keys are not being pressed and are therefore not in the passcode.
So look for the clean keys and try combinations from there. In a 4 digit (0-9) keypad, knowing the clean numbers drops the possible codes from 9999 to 24 (if my early morning math holds up).
Also helps the issue of someone looking over the shoulder of a valid person. Chances are they are just seeing the position and not the character pressed. So the keyboard changes and you actually need to know the character not just the old position.
So look for the clean keys and try combinations from there. In a 4 digit (0-9) keypad, knowing the clean numbers drops the possible codes from 9999 to 24 (if my early morning math holds up).
Also helps the issue of someone looking over the shoulder of a valid person. Chances are they are just seeing the position and not the character pressed. So the keyboard changes and you actually need to know the character not just the old position.