I have 2 devices H100 tapo hub & T100 motion sensor 

I have setup automation in tapo app to trigger/ring H100 when T100 detects motion.

this automation works fine when internet is available. 

when internet is not available(please note wifi router is still available/on) T100 on motion could not ring H100.

since T100 connects to H100 without wifi or internet on sub gigahertz band it should work without internet, is this not true ?

As per my understanding internet is needed only to push notification on tapo app and control devices from tapo app, but once deices are setup and connected to hub then internet should not be required. 

Please clarify.

I am using this setup for home security/intruder detection & if it can not work(ring H100 alarm) on local network using only wifi router(without internet) then its useless to me.