Watch out for the doors!
'Attenzione' — at-ten-TSYO-ne. The 'zi' produces a 'ts' sound, not 'z'.
This is an automated announcement you will hear on every metro departure. You can also use it yourself to warn someone who is blocking the doors.
'Attenzione' is an exclamation that functions as an imperative warning. 'Alle' is the contraction of 'a + le' (to the). The phrase 'attenzione a + noun' is extremely common in Italian warnings and public announcements.
Le porte si chiudono!
The doors are closing!
Announcement version describing the action.
Si allontani dalle porte.
Please step away from the doors.
Formal instruction from staff or recording.
Faccia attenzione!
Please be careful!
General formal warning; 'faccia' is the Lei imperative of 'fare'.
On Rome's older metro trains, doors close with little warning. On Milan's newer automated trains, a loud beep signals closing. Always let passengers off before boarding — standing in the doorway is considered rude.