Do I need to tell you how annoying false alarms are? Of course not. You have no doubt been disturbed countless times by car alarms, burglary alarms, fire alarms, etc. And the false alarms are so common that you probably don't even think of the possibility that the alarm could indicate actual danger.
An alarm has no value if it sounds so often that people lose confidence in it.
Some alarm systems can make false alarms repeatedly as long as the technical fault that caused the alarm has not been fixed. This should be avoided by turning off the sensor that caused the false alarm until the problem has been fixed. An alarm should always stop sounding after a reasonable time if nobody stops it manually. It should still have a visual indication that an alarm situation has occurred, though.
The volume of the sound should be so high that everybody can hear it, but never so high that it is painful, causes panic, or prevents talking.
Surveillance staff who have nothing to do but waiting for alarms get dull and demoralized if they have nothing to do. So dull, in fact, that they may fail to react promptly and adequately when an alarm finally occurs. Their job has to be organized in such a way that they have plenty of other work to do when there are no alarms, and they should participate in regular drills to rehearse what to do when an alarm occurs.