Sorry I pasted a wrong formula.
OID doesn't give you the percentage of CPU utilization, so to calculate CPU utilization percent take two samples, calculate the delta, and calculate: ((<DeltaTmTotalCycles> - (<DeltaTmIdleCycles> + <DeltaTmSleepCycles>)) / <DeltaTmTotalCycles>) * 100
Monitoring tool normally monitors F5 IP, so if the IP is not reachable the F5 become "red". Just like F5 have monitor on Pools/members/nodes used by LTM.
If something is going wrong inside F5, TMOS generates internal alarm/logs, so can F5 can generate SNMP Trap or send "error log" to remote syslog servers or send email using an SMTP server.
So if you're asking "How F5 is able to send alarm if something is going wrong?", you can use one (or more) of the 3 options (SNMP Traps, remote syslog, email using external SMTP server).
BR