HSL’s ticket inspectors may issue a penalty fare to a passenger travelling without a valid ticket.
You must have a valid ticket before you board a bus, tram or commuter train, or enter the metro payment area. When using the HSL app, the ticket must be on your phone before you board a vehicle or enter the metro payment area. If you buy your ticket with value on your HSL card, you must buy the ticket at a card reader at a metro station or immediately after boarding a bus, tram or commuter train.
When travelling by the metro, you must have a valid ticket already at the station. The metro payment area is clearly marked at each station. Typically, the payment area begins at the card readers at the top of the escalators to the platforms.
Read more about HSL’s fares here
Read more about the penalty fare here