What is apcupsd?
"Apcupsd can be used for power mangement and controlling most of APC's UPS models on Unix and Windows machines. Apcupsd works with most of APC's Smart-UPS models as well as most simple signalling models such a Back-UPS, and BackUPS-Office. During a power failure, apcupsd will inform the users about the power failure and that a shutdown may occur. If power is not restored, a system shutdown will follow when the battery is exhausted, a timeout (seconds) expires, or runtime expires based on internal APC calculations determined by power consumption rates. Apcupsd is licensed under the GPL version 2." 
First, emerge sys-power/acpupsd:
# emerge apcupsd # equery f apcupsd
 Configuration and Runlevel Registration
Edit your /etc/apcupsd/apcupsd.conf properly.
To start apcupsd, run the following:
# /etc/init.d/apcupsd start
To add apcupsd to the appropriate runlevels, execute the following commands:
# rc-update add apcupsd default * service apcupsd added to runlevel default # rc-update add apcupsd.powerfail shutdown * service apcupsd added to runlevel shutdown
 Check UPS status
Finally, to check on the status of acpupsd, run the following:
# apcaccess status # tail -f /var/log/apcupsd.events