Comb Communications makes a distinction between the two types of PINs, ie: PIN: A permanent 4 digit secret number that residents use to gain access to the complex. TAP: A temporary 5 digit secret number that guests use to gain access to the complex. The Tap-Tap keypad is very secure and cannot be bypassed in anyway as no codes or PINs are stored on the unit, and neither is the controlling relay on the keypad. The Keypad is simply a means of sending TAP. PINs to the MK II Plus Intercom. The Intercom decide if the PIN is valid or not. A further benefit of the external keypad is that the regular resident PINs can be entered on these keypads. IC-CMKIITAPTAP