I installed apcupsd and testing it I don't see any message being broadcasted via wall when I unplug the power.
setting: UPSCABLE 940-0024C usb UPSTYPE usb DEVICE POLLTIME 30 LOCKFILE /run/apcupsd SCRIPTDIR /etc/apcupsd PWRFAILDIR /etc/apcupsd NOLOGINDIR /etc ONBATTERYDELAY 10 BATTERYLEVEL 10 MINUTES 5 TIMEOUT 0 ANNOY 45 ANNOYDELAY 90 NOLOGON disable KILLDELAY 0 NETSERVER on NISIP 127.0.0.1 NISPORT 3551 EVENTSFILE /var/log/apcupsd.events EVENTSFILEMAX 25 UPSCLASS standalone UPSMODE disable STATTIME 0 STATFILE /var/log/apcupsd.status LOGSTATS off DATATIME 0 -- Thelma