Elementary school - Had round Lathem clocks and a Dukane PA system, both installed upon the school’s first expansion in 1986. The old wing had the clocks and speakers separate (you pulled strings on the sides of the speakers to call the office), while the new wing had tall combination units with a clock, a speaker, a call button, light switches, and a thermostat. The bell was generally a steady tone that sounded for 5 seconds. The one I remember for the majority of the time was a middle-pitched G-note (I think). I remember that it was higher pitched when I first started there in kindergarten, and in my last year (8th grade) it became lower-pitched and a bit overtly loud. It also became slightly higher pitched for a short time later on (I want to say 4th or 5th grade) - the first day that tone was used, they also seemed to be experimenting with other tones during the morning (a quick chirp and a very high-pitched raspy tone), or perhaps they were having problems since the bell then stopped sounding for two periods before the slightly higher-pitched tone returned. The year after I graduated, when the school expanded, the bell became an intermittent “Bing… Bing-bing… Bing-Bing”, also a bit on the loud side.
First high school - Built in 1970, the school had a Simplex synchronous clock system and a Dukane PA system - the controls for both were updated over the summer before my sophomore year. The bell during freshman year was a steady high C note, sounding very similar to the common “bleep” tone used for censorship (laughter would ensue when the bell would interrupt a PA announcement). Sophomore year, it became three lower “F” notes sounding over the course of five seconds. The PA system had the Simplex units with square clocks (many of which were either frozen or displayed the wrong time, even after the upgrade) and speakers next to each other. There were Dukane-branded phone handsets on the walls of each room that would initially be used to talk privately to the office, but after the upgrade, the receivers essentially functioned as call switches and communication would take place through the PA speakers. Then the next year, the receivers were removed in favor of a telephone system installed throughout the school, leaving the PA system for one-way communication only.
Also worth noting, the gym, cafeteria, and band room were in the elementary school building next door. This had a Standard synchronous system from 1960 with round clocks and 6-inch Standard vibrating bells. Don’t know a lot of details about the PA system - the speakers were flush-mounted and separate from the clocks, and there didn’t appear to be any two-way communication capability.
Second high school - At the time I attended, it had an old Standard AR-2 impulse clock system (no second hands) with round clocks. I don’t remember as many details about the PA system, but I believe Rauland made the speakers which were separate from the clocks and did not have two-way communication. The bell tone was similar to the second one from my first high school, but faster (five “bings” in five seconds). But there were also Standard 6-inch bells behind grilles (alongside the original alarm horns which had been disconnected about a decade earlier) in the gym, cafeteria, and auditorium areas, as well as 8" (I think) bells outside the school with protective metal casing. These sounded simultaneously with the PA tone. Since I graduated, the PA and clock systems have been upgraded - there are digital clocks now, there’s PA speakers outside the school, the bell was a different intermittent tone the one time I heard it, and the actual bells no longer sound.