that have children/ grandchildren heard of this,
We were having dinner with our son ,d -in l and Grandson (11) mum asked him do you have fire drill at school, yes he replied---
1 bell is a test
2 bells is a fire drill
3 bells is a fire and to evacuate
All pretty much standard until he went on to say
6 bells mean school on lockdown ,intruder alert and to hide under your desk