Late 2014 Mac mini running Sierra connected to an APC BackUPS Pro 900. No special software has been installed to support the UPS.
At the moment I run
pmset every minute to determine the power source, and trigger actions based on the results.
However, a dialog window pops up as soon as the Mac switches to backup power. I'm wondering if there is any way I can trigger based on anything else, given that macOS seems to be able to do so.