The scheduler is a good way to get email sent on a regular basis. You can schedule reports at a given interval. If you don't get a report, you know something is potentially up.
Alternatively you can run a bash script to down an interface via snmp or port and run it at a regular interval via cron if using Linux server. Then use alarm manager to alert you when said action took place.
Something like
In Crontab
0 10,12,15,18,21 * * * /root/scripts/NMCCronCheckin
Then the script would just
/usr/bin/snmpset -v 3 -a SHA -A "SNMPPassword" -l authNoPriv -u "Account" "Switch IP" .1.3.6.1.2.1.2.2.1.7.22016 i 2 [22016 is an interface I would want to down]
/bin/sleep 240 [240 is seconds of a poll cycle, change to whatever you poll at]
/usr/bin/snmpset -v 3 -a SHA -A "SNMPPassword" -l authNoPriv -u "Account" "Switch IP" .1.3.6.1.2.1.2.2.1.7.22016 i 1