Android Question Start with firebase

your arduino sends a message to google which is relayed to your firebase app. the messages don't go directly from your arduino to your phone. any networked device can send a firebase message. only subscribers to the message can receive it. google, as always, stands proudly in the middle - reading, scanning, watching, storing. if you had a spare phone, you could run a little server on it to receive messages from arduino. then your spare phone could send an sms to your regular phone. but then, google would miss you and start looking. if you're expecting trouble from your gas line, maybe you need both solutions to be safe.