How do maids know when to enter a hotel room?

I'm just curious because when I leave a hotel room and come back everything is fixed like the bedding's. How do they know that were not there?

When you walk out of the hotel, the reception staff know what room you are in and let the maids know that.

I used to think the same thing, thinking to myself they are so clever and wow look how clean the room is, they do a really good job, I always leave a tip for them.

Its called Housekeeping ! They normally have a specialised timing for all the housekeeping employees to go floor by floor to clean the rooms .

If you dont want them to enter your room you can simply put a little flag on your door (That all hotels have) which says privacy or dont disturb .

Well I'm not sure about that, but when I stay in hotels I don't like the maids going in there (I'm afraid they might touch or take my belongings) so I always put up the "Do not disturb" sign right before I leave.

they normally ring the bell first and if there is no answer or no sign on the door they can enter the room.

We have hidden cameras in your room. We know when you come and go!!!!!!!!!!