Never leave your key card with its folder. When you are first given your key card, it usually comes with a key folder that has important information like your room number and the hotel address. Once you have memorized your room number, keep the folder separate from the key itself. This way, if the key card gets lost or stolen, your room will still be somewhat secure since whoever gets it won’t know your room number. If you want to be sure, if this happens, ask the front desk to change the code on your door and to give you a new key card.