My colleague last time said he encountered hantu knocking in his hotel room at his bedside table as soon as he turn off the lights. When he turns on the light, no knocks. Kept repeating till he felt so scared he hid under the sheets till morning. In the morning, he realised his room key was still at his door so anyone could enter anytime he was sleeping.

So I'm guessing the ghost wasn't able to speak chinese/english, so while being a kind spirit not wanting to scare him by revealing itself, it wanted to tell him about the key at the door, but didn't know how, so it chose to keep knocking, keeping him from sleeping, hopefully he goes out of the room to complaint to the reception.