Prague's contactless screens are ticket machines, not London-style fare gates. On trams and urban buses, a tap buys a timed ticket that begins immediately. A paper ticket from another machine may instead need one deliberate stamp. Knowing which object you bought prevents both double validation and an unstarted ride.
First identify the kind of ticket
The tram screen lives near the middle
Prague Integrated Transport says the onboard touchscreen terminal sits by the middle door in trams and by the second door in urban buses and trolleybuses. It accepts contactless payment only. The result is a ticket tied to its printed start time, not an open-ended bank-card tap.
The yellow validator is for the unstarted paper
Tickets from conventional machines, information centres and ordinary ticket offices need validation. Stamp once, in the arrow's direction, before crossing into the metro paid area or immediately after boarding surface transport. Stamping a time-printed terminal ticket again is unnecessary.
The phone has a one-minute blind spot
A ticket in the PID Lítačka app is active but not yet valid during the first minute after activation. Activate before the vehicle arrives or before entering the metro's paid area. Once active and past the countdown, it can remain valid without a data connection.
One timed ticket can cross modes
Prague short-term tickets are based on time, not on one vehicle. Within the ticket's validity and covered zones, a trip can combine tram, metro, bus, ferry or local train. Choose enough time for the whole connection, including the walk between platforms.
Regional buses follow a different door
Suburban and regional buses generally board through the front. The driver can sell a ticket and accepts coins, notes up to 200 Kč and contactless cards according to PID guidance. That ticket is already time-printed and valid, so it does not need a second stamp.