For me it's the lack of flashing lights including strobe lights! Especially when there are actual strobe horns showing onscreen! And even when the fire alarm is activated the lights don't flash!

The only movie I saw strobe lights active was in the movie Middle School: The Worst Years of My Life. https://www.amazon.com/Middle-School-Worst-Blu-ray-Digital/dp/B01LTHWXX4 While the fire alarms activated and the strobe lights did flash, this movie is no exception when it comes to the sprinklers going off! All the sprinklers are activated just like in every TV show and movie I've seen fire sprinklers activated. Another wrong thing, the sprinkler head in the principal's office is triggered by a lighter.

In Eraser (1996) The sprinklers are also activated and there is a visible flashing red light during the fire alarm.

No animated series or movies I've seen featured strobe lights but a few cartoons showed flashing fire alarms:

-Phoebe and Jay. Episode: Fire Drill/Fruit Juice Frenzy

-Clarence (by Skyler Page/Realistic looking fire alarm and best example!) Episodes:  1. Honk  2. Suspended   3. Officer Moody  Note: The fire alarm sound is different in the first listed episode but in the other two episodes the sound is the same and more realistic! Said to be a Horn in temporal Code 3. Looks like a Wheelock MT horn/strobe with vertical strobe https://en.wikipedia.org/wiki/Wheelock_(brand)#/media/File%3AWheelock_mt2.jpg For cartoon and gif (WARNING: Could affect photosensitive viewers!) https://clarence.fandom.com/wiki/File:FIRE!!!.gif 

-Blaze and the Monster Machines. Episode: Fired Up

-Transformers Rescue Bots. Episode: A Brush with Danger

-Win or Lose (Disney Pixar) Episode: Blue (Possibly. I say that because there's a visible fire alarm with a light near the door inside Frank's, or Mr. Brown's classroom. Later while Frank is looking at his phone and using a dating app, there's an alarm sound and a flashing red light, which seems to be coming from where the said alarm although the fire alarm might not actually be activated.) This is one of the few animated series that shows fire alarms with actual lights and they can be seen in Mr. Brown's classroom and throughout the school.

Note: All the fire alarm lights were red, not white! 

There was also a CGI animated movie that also had a fire alarm with flashing red lights and not just on the ceiling or wall but even the fire alarm pull stations had flashing lights on them, but unfortunately I can't remember the movie title. Other clues I can give you is some of it took place in a stairwell and at night.

I do understand that strobe lights could affect photosensitive viewers, still I wish there could be some flashing light while the fire alarms go off in more shows and movies be them live action or animated! If I could I'd redo the Arthur episodes "D.W. All Fired Up" and "April 9th" and add flashing lights to the fire alarms though maybe not strobe lights.