[Muromec]

It will bill your 4 EUR (on a tram/bus) or the whole 20 (or something on a train) instead of the actual journey price if you forget to checkout. Pretty sure it can decline cards for insufficient balance too. Not sure the entry gate blocks the amount.

Actual chipcards don't bill you at the end of the month either -- they reload a fixed amount through direct debit (which takes a few days) the moment your balance crosses zero. If the direct debit isn't setup for a card (because it's not a personalized card) or the debit was rejected, the card is blocked.

For business chipcards cards it works somewhat the way you described.