Virtual Fire Detector

I would like to create a virtual fire detector device that will allow integration with other smoke alarms inside of the Smart Home Monitor. This virtual device would allow the user to choose temperature sensors that would act as a heat alarm. The idea would be to choose a number of sensors in a given space and compare those to a high threshold or temperature acceleration. I know I can create an automation based on temp, but I want it to appear as an alarm within the Smart Home Monitor itself and allow full alarm integration. I am also interested in creating a “freeze detector” that acts similarly.

Any suggestions on pre-existing apps/devices? Given that groovy is going away, would it still make sense to write a new SmartApp?