I just answered you on the same topic in another thread:
Smartthings Compatible Smoke/CO Detectors - #8 by JDRoberts
As far as the built-in security features in the smartthings app, the one in the classic app was called SHM (Smart Home Monitor) and the one in the current V3 app is called STHM (SmartThings home monitor). They are similar but with slightly different features. This is a smart app which is available to most smartthings customers, although it may be region locked out of a few countries, I’m not sure.
However, it’s really important to understand that these features are completely dependent on the smartthings cloud being available. Even notifications on your own phone. Even being able to change from armed to disarmed. So it’s not a UL listed security system and could not be. It’s OK for convenience notifications if you want that, but it’s not something you should bet your life on. The company says so themselves in the product usage guidelines, although most people don’t read the fine print.
If you want a security system, get a security system, like Ring or Abode or Simplisafe.