Which department should I complain to if there are no protective bars on the hotel windows?

You can complain to the fire department. Or you can complain to the industrial and commercial administration department or the housing and urban construction bureau. Failure to install safety guardrails is a potential safety hazard. Bay windows without guardrails are the most harmful to children. Children aged two to six who are just learning to walk and are extremely curious often go to balcony bay windows and other places to play naughty. They can play, climb up and down, and children are extremely curious about the outside world. It is easy for accidents to happen with such a bay window.