I left my keys in the room.
'Chiavi' — KYA-vi. Two syllables; 'ch' before 'i' is hard like 'k'; the 'ia' is a diphthong.
Say this to hotel reception when you are locked out of your room. A replacement key or a staff member to open the door can be requested.
'Ho lasciato' is the passato prossimo of 'lasciare' (to leave behind). Note: 'lasciare' means to leave something in a place; 'partire' or 'andarsene' means to leave in the sense of departing. 'Nella stanza' (in the room) uses 'nella' = 'in + la'.
Sono rimasto fuori dalla stanza.
I am locked out of my room.
Describes the result rather than the cause.
Può mandarmi qualcuno ad aprire?
Can you send someone to open it?
Request for a staff member.
Ho perso la chiave della camera.
I lost my room key.
Use if you cannot find the key at all.
Italian hotels increasingly use key cards (tessere magnetiche) rather than traditional metal keys. If you lock yourself out, you need to present ID at reception to get a replacement — this is a standard security procedure to prevent unauthorised access to rooms.