Your ticket IS ONLY VALID up to the border of the tariff community, even if you enter another tariff community in which FAIRTIQ works. The journey computation will stop at the border of the tariff community even if you check out at a later stage.
If you enter a tariff community where FAIRTIQ works too and the train does not stop at the border, your FAIRTIQ ticket becomes invalid after the last station before the border. Checking out for a couple of seconds and checking in again just after you have passed the border within a moving vehicle will not give you a valid ticket.
If you leave the tariff community, you have to buy a valid ticket through a traditional sales channel.
Where can FAIRTIQ be used?