A.L.
sometimes although fears manifest themselves in other aspects of our lives such as for example, your grandson fearing firing alarms, there could be something more to it.. that sound might trigger something deeper.. Can you find a place that is very calming for him and see IF when he is in that calmer state if he will open up to you.. just ask simple questions and see if he can try and talk about how he feels. DON'T make it just about the fire alarm, but see if he expresses other feelings around it.. the fire alarm may simply be the trigger to something bigger or not...he's young and therefore cannot express in depth why the alarm evokes such emotion in him. Truly, it may not be the alarm. I truly think the alarm is only a symptom... Could be that your grandson having heard that alarm equates being left at school with that sound??? I mean the subconscious mind tries to make sense of our every day life even if it means being irrational... like >> alarm = being left= feeling vulnerable = ANXIETY and once anxiety kicks in... it's hard for a little one to know how to handle it.. in a way it's good that he cries in that he is releasing some of that anxiety physically and emotionally..
I would see this less as the alarm but more about anxiety... which many small children do experience when first entering preschool..
I wish you the best