We had an incident (on my last day in the office while finishing my notice period) where a guy came in to the building and used an aerosol and lighter to set off the fire alarms and unlock the doors, so he could then get in to the office and proceed to threaten everyone with said homemade torch.So annoyingly an intruder could just break a fire alarm to unlock the doors
The roller shutters were down over the emergency exit doors too, so we were backed up to them waiting for them to very, very slowly open as he kept walking towards us, occasionally burning stuff on the way. I'd like to think procedures have changed since I left.