Have wondered about those, not sure how hard it would be to connect to the whole house. A single ring I could probably do quite easily. Think you need proper sockets/plugs to do it safely rather than the technically works but you may die if you touch the pin kinda cable. Then just flip the circuit breaker to remove that ring from the grid.
But that wouldn't cover cooking or my heat pump. Not sure if that could properly be done as a DIY job.
Though doing 1 ring from the battery would make it pretty easy to measure my non cooking/heating energy usage. Suppose lighting is separate but that should be all LEDs anyway.