I have also hacked a simple €10 hardware store smoke alarm with an ESP8266 to protect my home. I have CCTV, Wireless Switch and all the POE power and data for my TTN Gateway in the attic space. A fire could destroy the roof structure here before we would be aware so I built this.
There is a pin on the control IC of most smoke detectors to allow sympathetic alarming (such as in shared spaces of an apartment complex). I used this pin of the IC to drive the enable input of a mini buck converter which then generates the 3.3volt supply for an ESP01 module.
The ESP01 module boots, uses a static IP address to connect to my home router and pushes a message to our mobiles and Chrome extensions via Pushbullet. Total time from alarm to phone is circa 3-6 seconds and is 100% reliable so far in testing.
There is absolutely no technical reason why this could not be LoRaWAN. I chose the WiFi as it is slightly more persistent and to push a message involves less routing (fewer possible flaws in an already NOT fail-safe system).
The quiescent current (we love this number here!!!) of this system is only that of the detector circuit as the WiFi module is off unless the alarm is triggered.