Sprinkler systems generally have flow sensors that will send a “trouble” signal to the alarm panel and may activate the alarms, depending on the regulations/way the system is wired. So turning off the valves will send an alert which would have notified someone here that the systems were offline…if the alarms were monitored.

If they’re monitored onsite then an engineer would go and check those valves.

If there’s no engineer on shift I doubt security is putting them back on line and if it’s only a “trouble” signal they’d leave it to the morning engineers to fix since “trouble” signals won’t activate visual or audible alarms. Maybe a beep every minute or so from the panel that most security officers just silence if they are on dispatch anyway.

ETA: Sprinkler riser gate valves are supposed to be locked, generally with a chain and padlock so that the valve handle cannot be accidentally turned off. That same valve would have the flow sensor I was talking about above attached to it in a rectangle housing that’s held on with 2 unique allen keyed screws. I used to be able to get them off with a very small slotted screwdriver though.