I've been using Google Home Preview for a week. I turned on presence detection. In the feed I also see that my smartphone is recognized as being present or absent, but the status does not change automatically in the Home app. Thus, the cams are not automatically activated or deactivated. Furthermore, I can't find a way to configure the processes "At home" and "Away" anywhere. I can't find where to set which cameras should be activated and which shouldn't. I'm really at a loss.
I’m having the same issue too. Spent the last 2 hours trying everything but I’m not getting the option to trigger automations with presence sensing. Sorry this doesn’t help you. It just thought I’d put it out there