I'm not sure if my team is a crazy exception, but here's how our on-call works: We're usually on from Monday-Monday (with exceptions if we say, don't have time on Wednesday or something), but every team decides the time on their own. During work-hours, every team member is responsible for responding to alerts (but usually, only the on-call engineers will carry their company-provided phones and are the first to respond).

Outside work-hours? Most alarms (if they happen) are due to bad alarm configurations. Because nothing ever happens. There was one alert this month, and it was because a randomly generated ID contained the string "ERROR" and was logged due to a warning.

I know that my company isn't the "biggest" (only a few hundred requests per minute) and traffic amount is mostly correlated to usual business hours in my country, so there's just not much happening at night (but never zero traffic). Still, I'm always surprised that other companies seem to have really stressful on-call shifts, because the most annoying part to me is having to carry my laptop if I leave my home for more than 20 minutes.