Sounds similar to the UK system that was tested on 23rd April this year. Technology is based on the Cell Tower, not SMS or an APP, which allows for localized incidents as well as country wide . I hope someone in Thailand remembers to transmit the message in English as well, as with all the other Thai language messages I get, they go straight in the delete bin.
The UK test was expected to target 90% of the UK mobiles, reality was closer to 50% due to technical issues, plus the fact only 88% of the UK at the time was 4/5G capable of reception (rural and dead-spots). Solution is based on a 4/5G signal and users running the latest Operating System on Apple or Android. If you use WiFi calling, then no message received. Another factor to consider is power for the cell towers, as from recent storms in the UK, localised power outage has effected mass communications. Maybe the old days of a CB-Radio and a 12V car battery could be the way forward (or backwards)!