In case of ticket inspections by ATAC personnel, you´ll just have to show them your card or the device used for validation. The ticket inspector will simply check your card number.
If you travel on a Cotral surface or railway line (bus, Metromare or Roma-Viterbo railway - urban route) you must necessarily have downloaded the Atac Tap & Go ® application (only on Andorid devices equipped with NFC technology) and show it to the inspectors.
If you are on board of Trenitalia regional trains (second class urban route), in case of controls you will have to display the credit card used for the payment or communicate part of its PAN (first six or last four digits of the card number).
Remember to travel within the validity limits of your ticket. To avoid potential penalty fares, remember to "tap" your card each time you change means of transport. Taps made within the validity period of the ticket do not count as a new payment. Therefore, always remember to "tap" on surface vehicles, before the 100 minutes run out.