Sprinkler myth is all wet
All the sprinkler heads going off at the same time only happens in bad movies. Each sprinkler head has a heat activated trigger that keeps the water valve in each head closed unless the air temperature at that specific head rises above the trigger value. This system was designed a long time ago when elec-trickery was understood to be unreliable in a crisis, so no common signals for false alarm disasters.
Still a dumb idea to use water, when CO2 is cheap and plentiful. Too bad the horns that announce its release are so loud the vibration can damage the equipment (hard drives mostly) it is there to protect.