In Ecostruxure Secure Connect Advisor, in the Tab "Audit" of the GateManager, there is the possibility is see when the appliance is connected.
However, only the status "Appliance Connect" is visible. The status "Appliance disconnect" is not reported in the history
In the following screenshot, only "Connect" is visible

This Article is applicable for Ecostruxure Secure Connect Advisor
If the use want to be informed when the appliance is disconnected, there is a possibility using Alert function
In order to create the Alert function, need to have a GateManager Premium Access (ref: VJOCNTGMPREM)
Then right click on Domain name, and select "create alert"

Select the appliance

Result

However, only the status "Appliance Connect" is visible. The status "Appliance disconnect" is not reported in the history
In the following screenshot, only "Connect" is visible
This Article is applicable for Ecostruxure Secure Connect Advisor
If the use want to be informed when the appliance is disconnected, there is a possibility using Alert function
In order to create the Alert function, need to have a GateManager Premium Access (ref: VJOCNTGMPREM)
Then right click on Domain name, and select "create alert"
Select the appliance
Result