DHCP4 - Status... what is that?

[tre4bax]

When you look at the leases in DHCP there is a table one of the columns of which is labelled status.  What does this actually do?  It seems woefully inaccurate at saying whether a device is actually online or not.  It shows my main router as Offline when clearly it can't be and it shows my switched off mobile phone as connected.

Is there a way to get good information at what is actually connected at what time?