What's that Sound?

Schools Locked Down After Shots Fired Report

I am aware of schools now featuring ASA (Active Shooter Alarms) systems that are to warn all students and staff there is thought to be a Shooter running lose on campus.

But what do the Alarms sound like?

Are they a Whoop-Whoop like a submarine dive alarm, is it a loud Buzzer with tones like a Fire Station staff alert, or a Hi-Lo horn like the European Police cars?

Perhaps the TV News folks might make us aware as the next time when watching my grand daughter perform in a dance recital and some Alarm sounds I would like to know if I am run for cover or just follow her to recess?