An ASCII string containing the 3 digit Decimal code
representing the current active message from the
System Message Register. Each code should remain active
for a minimum of 15 seconds. However, in the worst case
scenario, a code could be cleared after only 5 seconds.
It is recommended that this object be polled at least
once every 4 seconds in order to get the most accurate
representation of the current UPS System Message. If the
Network Card is unable to determine the value of the
System Message Register, this variable is set to
'UNKNOWN'.