An interesting option that comes to mind would be having pre-specified codes that contain client-side (pre-baked in) messages, something like '1 - Wildfire alert: ...; 2 - Heavy rain; 3- ...; 1023 - False alarm: please disregard ...', possibly with another severity parameter to modulate messages etc.. Then at least no one could simply hijack the system to send arbitrary messages (only one of pre-chosen alerts).

"Sorry men with guns, the most we can do is send one of those messages."