My current company has a rotating week of oncall. Happens every 2 months or so. Oncall gets paged first and is expected to be available 24/7. But if they escalate further, whichever dev or manager it gets escalated to is expected to be available 24/7
By 24/7, I mean, they don't tell you that you're allowed to sleep. They just fired a manager for not being willing to wake up in the middle of the night for pages
Edit: also a bunch of people on our team think it's normal to ping and ask for help on non oncall stuff outside of business hours (like 7 or 8)
Edit 2: I forgot to add, we are not paid anything extra for oncall (or any additional work time outside of business hours). It's salaried