I was "on-call" for many years...but unless it was a formal "on-call", no extra compensation...when I had to take the company pager or cell phone home, I got an extra 2 hours of pay per day for making myself available, but in reality, my job required me to be available 24/7 anyway...(I was the ONLY crane operator in the company, although there were 2 other guys who knew how to run the crane in case of emergencies, and they always had the option of an outside crane company)
I don't know of any law that requires them to compensate you for being "on-call" unless you're actually called back to work, (for us hourly wage-slaves) but you salaried-slaves probably get to work extra for free...😉