In my schools we just showed up at the school yard in the morning and lined up with our classmates when it was time to go into school in the morning. Same process at lunch time. During warmer months one of the gym teachers who helped organize and "officiate" sports games for the older kids during the lunch break would blow his whistle at the appointed time to let everyone know that they had to line up to go back into school.
Call me an oddball, but I don't understand why this process would require bells or loudspeakers.
Of course, things changed in high school, but only because the students moved from one classroom to another throughout the course of the day -- and therefore the automated bell system indicated the end of each period.
It wasn’t until 2 years ago my middle school started with bells. I liked it SO much better without.
One of the local elementary schools still has the old school bell in the tower. They use that for everything other than the fire alarm/tornado drill. Very sweet and quaint