When I was an SRE at Google our oncall was extremely serious (if the service went down, Google was unable to show ads, record ad impressions, or do any billing for ads). It was done on a rotation, lasted 1 week (IIRC it was 9AM-9PM, we had another time zone for the alternate 12 hours). The on-call was empowered to do pretty much anything required to keep the service up and running, including cancelling scheduled downtimes, pausing deployment updates, stop abusive jobs, stop abusive developers, and invoke an SVP if there was a fight with another important group).

We sent a test page periodically to make sure the pager actually beeped. We got paid extra for being in the rotation. The leadership knew this was a critical step. Unfortunately, much of our tooling was terrible, which would cause false pages, or failed critical operations, all too frequently.

I later worked on SWE teams that didn't take dev oncall very seriously. At my current job, we have an oncall, but it's best effort business hours only.