How do you avoid electrocuting a linesman? Don't products like a powerwall have a disconnect relay to ensure there is no backfeed?

I can't see how this product can backfeed to the household circuit safety/legally unless there is some technology I'm not aware of?

Can back feed when the grid is up. Can't back feed when the grid is out. It has an onboard relay to disconnect from the grid when there is an outage.

how can a device connected to a power point disconnect from the grid?