Not to trivialize natural disasters, but I heard from co-workers that if you're in Japan in a large public venue or meeting and everyone's mobile goes off at once, then everyone stops what they're doing and checks their phone, that's probably the earthquake alert systemwarning of a potential imminent quake.

Whereupon it is observed that no one ACTUALLY moves to a location of safety, instead they just stop moving and waits quietly for about 30 seconds, then resumes their business or activity. The explanation being that the alert gives just a few seconds warning usually, and so if it doesn't hit in 30 seconds, it was a false alarm. But if it does hit ... hmm?