It’s called being on call. It requires an hourly wage for the duration. That said, call pay is usually garbage (like $4/hr). I would posit that call pay should be minimum wage, or more.

This is no different that being required to pay out a lunch break if and when you’re required to remain available during said lunch break, can’t leave campus, or have to carry a live walkie/radio while “on break”. Federal definition of a lunch break defines it as “uninterrupted”.

My on call works with garbage pay but if I’m called in it’s automatically OT, even if that’s my one shift that week. Ofc, I’m Union. Even so, the stand at the starting line, available pay, should be at least minimum wage.