My salary, I guess.

Everybody on my team is required to do on-call once they have enough experience (except for the low budget offshore contractors who I wouldn’t trust to do it anyhow…)

We have 2 people on call at a time, 1 primary and one backup. You do a week on backup, then the next week you’re primary.

There’s no set time limits etc, but if you get sucked into some fire, people are reasonable about letting you take some time off the next day or whatever.

All in all, there are very rarely fires that happen inside or outside of normal working hours. Making the whole team be on call helps incentivize everyone to write more stable code since it’s your own ass on the line.