It's optional for all team members after around a year in, when they are familiar enough with the systems. The reason it is optional is that not everbody is able to do it - due to family, health etc.

There is additional pay for on call, based on numbers of days served. It does not matter if there were alerts or not - this is especially important: we don't get paid for work but availability. This incentives to harden systems and adjust monitoring well.

We also rotate regularly.

Each alert is followed up with incident report. If there was a lot of work, manager would give extra time off.

Hope it helps :)