There seem to be two ST solutions I find on this forum that at one time work with Nest Protect. NST Manager and My NXT Manager. But what is not clear is which one still works after the recent transition between Nest and Google, and for those of us who migrated over to google account. Any feedback would be appreciated. Not looking for any fancy feature, just enough where I can have the ST app notify me when it goes off when I am not home, similar to what it can do right now with their contact switches
Another option is to use an acoustic sensor that specifically listens for the UL listed smoke detector pattern and just integrate that. It’s very easy in the US as there is a zwave plus one from Ecolink with a certified ST integration:
That way you can use any smoke detectors, including Nest Protect, as long as they use the standard alert. No wiring required. 
https://www.smartthings.com/products/ecolink-z-wave-plus-firefighter-wireless-audio-detector
.
https://www.thesmartesthouse.com/products/ecolink-z-wave-plus-firefighter-ff-zwave5-smoke-and-co-audio-detector
Echo devices in the US can do the same thing with their Guard feature, but integration is then dependent on two clouds.