Nicolas,
I am not exactly sure what you are asking. It should be fairly easy to check to see if a value is greater that some level, and if so toggle an alarm. Are you asking for ideas on how to do this, or are you trying to modify a VI (Alarm Setup VI) and not able to? I have never heard of that VI, so I assume it is not built into LabVIEW. Give us a little deeper idea of what you are trying to do, and I am sure we can help you out.