You tap your card in the bus, when you pass by the tapping devices.
But monthly passes, for example in NYC, are expensive relative to single tickets, so adoption is relatively low.
If everyone has a monthly pass, fare evasion is less of an issue even in an open system. Fares are checked on a sampling basis with fines for not having a ticket.
Even in the US, monthly swipe passes have been a thing in even the systems that used tokens.