There is a lot of prior art here, the most relevant of which is probably APRS: https://en.wikipedia.org/wiki/Automatic_Packet_Reporting_Sys...

Newer digital modes do much better than this older AFSK system, but FSK does work pretty well. Some newer things to look into:

https://en.wikipedia.org/wiki/WSPR_(amateur_radio_software)

FT8: https://en.wikipedia.org/wiki/WSJT_(amateur_radio_software)

The more interesting modes (WSPR, FT8) are designed for high-loss channels, so have a lot of error correction. For example, I can use 5W of power, indoors, to communicate across the country with it. For high-bandwidth VHF channels, it doesn't matter what you use really. The goal would be to find something that already exists and is easy to integrate, and there are a lot of options.

Don't they already do this? I hear them all the time on my scanner? Hell they use a four digit unencrypted code to activate the emergency sirens.

I thought that fire trucks had a switch to activate the sirens by the drivers; I had no idea they were activated remotely by radio.

I was referring to the standalone towers in the Midwest. Maybe elsewhere. When I was a kid i would wake up on Saturdays at noon due to the siren. My dad also had a police scanner I could hear. One summer I put 1 and 1 together

All you need is a dtmf decoder and a small transmitter to set the off those large sirens on high poles throughout that sprinkle the country in small towns and probably large cities