http://www.slate.com/articles/life/travel_explainer/2015/08/charging_drinks_to_rooms_how_do_hotels_prevent_abuse_of_the_system.html

Hotel bars and restaurants are wonderful parts of the lodging experience. There’s nothing better than knowing that if you overdo it (whether accidentally or intentionally), you can politely stumble to the elevator and be in your bed, half-comatose and still fully clothed, within minutes. But not before you’re able to utter five powerful words: “Charge it to my room.” The room charge is clearly a convenient custom, but how is it kept secure? After all, a hotel bar can be brimming with activity at any given time, and presumably anyone could claim your number as their own. How do hotels keep the room charge system free from abuse?