What is this thing on the roof of the hotel room?

Usually a smoke alarm, used for fire prevention and safety.

It's definitely not a surveillance camera, because no one dares to be so blatant.

Life is always full of comings and goings, listening to the years, gently twisting the time left at the fingertips, and looking back at the deep and shallow traces of life printed in the fleeting time. Fortunately, the memory is still warm. Let the heart be as quiet as ever in the years. Remember that it is the most beautiful scenery in life.