I disagree... maybe 10% of hotels require a key to come up. Here in DC maybe 5% the most...
Some hotels do require showing a key to take the elevators after midnight, but that's also a minority.
Besides you can always tailgate, can you?
The provider can always dial 0 (zero) and find out, or go to the door and see a paper pasted on it with his room number and floor plan of the hotel. The address and room number are also on a sticker pasted on the phone of the room.
Asking and following signs you'll get to Rome.