Wanted to share this with you because it worked fine for me:
At first i tried an ESP-03 because it would have been tiny enough to be put into the case as well as the buck converter (MP2307) but I wasn’t able to solder it properly, so i took a wemos d1 mini.
I only had to cut the mounting a bit to hide it completely above the detector.
hello sir
nice work and thanks for the info sharing
have you noticed any problems from this device since you have installed it?
this would help me a lot thank you so much
No problems since then. It’s still working as it should. At least when I press the test button of the detector. Fortunately no fire until now. 
And what about the battery range? With WiFi technology normally it wasn’t go very long…
Did you read the article?
How to upgrade your cheap smoke detectors with cheap wifi (esp8266)
with esphome wondering if this could be done?
yes it could be done.
