APCUPSD has been my preferred UPS monitoring and controller software for many years. I’ve run it on everything from dedicated Raspberry Pi’s to VMs to on my desktop and now baked directly in pfSense.
Seeing as pfSense is plugged into my “backbone” UPS which also provides redundancy and filtering for my surveillance system and PoE switch, it only makes sense to have apcupsd, by way of pfSense, handle power-outage control. I have my UPS SMT1500RM2U plugged via USB-A cable into my Netgate SG-3100 USB-B running pfSense.
If you’re here looking for instructions on how to install a package in pfSense, you’re at the wrong spot on the internet.