Disable audible alarm on UPS
There is APC UPS Daemon can do exactly what you want:


  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.