It’s easy with Alexa devices, you can just trigger an Alexa routine (not a SmartThings routine). If you have a physical sensor which is visible in the Alexa app, you just use that as the trigger and then you can have your Alexa devices make an announcement when that sensor opens. And if your physical sensor is not visible in Alexa, you can use a virtual sensor on the SmartThings side. Very popular use case.
Here’s the community FAQ on that method:
FAQ: Can I trigger an Echo Action without Speaking to It?
But that one only works with echo devices. I know that at the time of this writing google routines didn’t offer all the same options, but hopefully someone else will know if there’s a workaround for those.