The main purpose of that bell is to sound the alarm if there's a fire and the sprinkler system is dousing it with water. A secondary purpose is to sound the alarm if water is pouring out of the sprinkler system and causing damage. You want it to work in either case, just to reduce damage.
Right now, something's wrong. Maybe the water is turned off to the house's sprinkler system so if there's a fire, the sprinkler system can't help control the fire. Maybe something's wrong so the fire alarm bell is just sounding off when it shouldn't.
I think you're going to have to bite-the-bullet and call a fire sprinkler company (not a lawn sprinkler company). They can help you (1) find out what happened and (2) fix or reset the system.