I used Raspberry Pi 4 which autostarts code when it is plugged in.
It sends a text message when an analog alarm bell goes off. Instead of a bell you can hoock it up to soemthing else. In my case the bell was 110V AC and I could not have directly conected it to the Raspberry Pi. For this reason I used an isolated dry contact relay that I connected to the bell. When the bell activated so did the relay and jumped isolated contacts. When this happened a previously pulled-up Pin on the Raspberry Pi went to the ground thus triggering the code. Another option is to use a buck converter. You would need to pull a Pin down via a resistor and trigger the code when the Pin is HIGH.
You may set time and day of the week limitations for the text messages. 10 minutes must pass before another text message may be sent. The system will sleep for as long as the triggering event is active, meaning the even must stop for the system to recharge. The purpose is to make sure the user will not be getting a new message every 10 minutes.
It sends a text message when power goes out, for this reason the development board must be on UPS. Your Wi-Fi router needs to be on UPS too, unless you have a wired internet. There is no time or day of the week limitation for this alarm.
It checks whether the system has internet connection. I bet there should be a better way of doing it. You must check for the internet connection otherwise it defeats the purpose of the system.
You may use GSM board then you will not need internet or TWILIO account.
