Sensor to know when a wire loop is cut

Hello,
It may be a stupid question but yet I haven’t found the solution.

I know and use some manageable NC/NO relay that we may operate on HomeAssistant by different way, basic 220V switch with Sonoff or even 8 ways relay controlled over ethernet.

But, what when we need to the opposite ?
My idea would be to have a wire loop, and be informed whenever this loop is cut. So I need a sensor able to have the info ‘Open’ or ‘Closed’

Seem pretty easy, but I’m missing the solution