Software-based contact debouncing methods are usually based onto a multiple polling with simultaneously statistics storing. The simplest method is a similarity counting algorithm, that continuously and periodically polls the contact. If the current instant read is equal to previous, counter increments, otherwise, it clears. The contact considered as a trust closed-up, when the similarity counter reaches some predefined threshold value. An improved method consists in denoting one of a contact states as a desirable (target), which is difficult to get into (needs a multiple equal values, which have inextricably inputted during threshold period) and easy to leave (a single contact conjoin value leads to reset of trust state). In this case, a Mealy finite-state machine (FSM) approach is suitable.