I saw this on the ceiling of the hotel room. Is it a smoke alarm or a camera

This is a smoke alarm, and the hotel will not install a camera on the ceiling, because it is an invasion of others' privacy and an illegal act. For example, if someone smokes in the room, or there is too much smoke in the room for other reasons, the smoke alarm will call the police. If the alarm status indicator is always on, there will be no sound at the scene when the alarm is given. Because the host computer has a sound and light prompt, the fire center will accept it, and then there will be staff to check and handle it.

When the smoke alarm works normally, most brands of smoke detectors have flashing lights, which means that the controller is patrolling the detector to check its working status.

The red light of the camera is an infrared camera, which images when the light is insufficient at night. It's a bit like the infrared imager used by the military in the movie.

Extended data

According to the sensors used, smoke alarms can be divided into ion smoke alarms and photoelectric smoke alarms.

1, ion smoke alarm

There is an ionization chamber, and the intensity of the radioactive element americium 24 1(Am24 1) used in the ionization chamber is about 0.8 micro-Curie, which is in an electric field equilibrium state under normal conditions. When the smoke enters the ionization chamber, this equilibrium relationship will be destroyed, and the alarm circuit will alarm when it detects that the concentration exceeds the set threshold.

2, photoelectric smoke alarm

There is an optical maze in which an infrared counter tube is installed. When there is no smoke, the infrared receiver tube cannot receive the infrared light emitted by the infrared emitter tube. When smoke enters the optical maze, the receiving tube receives infrared light through refraction and reflection, and the intelligent alarm circuit judges whether it exceeds the threshold, and alarms if it exceeds the threshold.

References:

Baidu encyclopedia-smoke alarm