I'd rather have Bluetooth, in a mode that allows for multiple users in a stateless way(Anyone can connect to it if they are nearby, the device doesn't know any secrets, etc)
Connect to it as a GATT server, send your message, and you don't even need LoRa at all if both phones are on the same hotspot.
No setup or connection, just put the sealed box with the solar panel somewhere and everyone in the 500' circle is now connected to the world.