What should I do if my hotel key card is missing?

It doesn’t matter, the hotel key card is just a magnetic card. When you check in, the waiter will enter the room information and the door will open. In theory, every card in the hotel can open your room door. The front desk usually has hundreds of them on hand. Just tell the front desk if you lose them and they will reissue them for you. Generally there is no charge. Be sure to inform the front desk, otherwise whoever finds it can also open your door.