Why does hanging something on the fire sprinkler in a hotel room cause the emergency fire fighting system to start?

Generally, the rooms in small hotels are very small. It is estimated that each room should be equipped with a smoke detector and a sprinkler, and the aisle should be equipped with smoke detectors and sprinklers. Generally, the distance between smoke detectors is not more than15m, and the nozzle is not more than 3.6m.. Then, manual alarm buttons and audible and visual alarm should be installed in aisles and stairs, with a distance of about 50 meters. The number of hand reports and acousto-optic signals is the same. The most important thing is to consider the water used for self-spraying. If there were fire pools and high-rise fire water tanks in the previous building, it would be good to save a lot of money. Just add a wet alarm valve, five water flow indicators and five signal valves (1 on each floor). In the alarm system, six control modules (five are to cut off the lighting by layers, 1 is to control the fire pump) and 10 monitoring modules (water flow indicator and signal valve for transmitting signals) are added. So this system will work.