Fire Alarm Trouble

For some reason, one of our fire alarms has been randomly "alarming" for about 5 seconds every few hours.  It's hard-wired in, so it's not a battery thing.  Daddy hasn't had the time to figure it out, so we've been dealing with it for a few days.  Finally, Mason decided to tackle it.  Talking to Daddy he said, "It must be the toilets causing the alarm.  If the toilets don't work, then the alarm goes off."   And with that, he checked the toilets by flushing them all.   When done, he returned, "nope, I guess that wasn't it..they all work".