What is the red light on the circular device on the ceiling of the hotel?

Smoke alarm. The smoke alarm is usually a circular device with a diameter of about 10 cm, which is attached to the ceiling. Under normal working conditions, a small red light flashes. So the circular device on the ceiling of the hotel has a red light, which is a smoke alarm. Smoke alarm is one of the most important means to prevent fire, and its function is to detect whether there is a large amount of smoke causing fire.