There is something on the roof of the hotel. What is this? It's still glowing.

Smoke alarm, also known as fire smoke alarm, smoke sensor, smoke sensor, etc. The power supply is supplied by the bus, which can be connected with multiple buses to form an alarm system and communicate with the fire alarm controller through networking. There is no sound at the scene when the alarm is given, and the host has an audible and visual prompt. This kind of smoke alarm device is generally called smoke detector. Smoke detectors are divided into areas with and without address codes.