well, i used to work for a fire protection company over on the east coast. ive done some inspections, and they are usually looking for broken sprinkler heads or damaged heads. The best thing you could do would be to tell them that u dont want anyone in ur closet, and if there is a head in there just tell them that its ok, and that the head looks fine, no leaks or rust stains. If they say they need to look in there or need to get in there. lol, tell them you would like to move a few things before you have them enter. or just lock it. if its locked they cant do anything. they will prolly ask " is there a head in there" and if so just say no. lol. but yet again, i dont know the Fire codes for where you live.
Is there a head in the closet?