Alert fatigue or alarm fatigue is when someone is exposed to such a high volume of alerts that they become desensitized to them or overwhelmed and unable to respond to alerts appropriately.
They end up missing true positive alerts altogether, getting around to actioning the alert too late, or misdiagnosing a true positive alarm as a false positive.
A practical example of alert fatigue would be pranksters repeatedly pulling a fire alarm, which in turn desensitizes people over time. Eventually a real fire breaks out, and no one takes it seriously until it is too late and they are trapped inside a burning building.
The Boy Who Cried Wolf is a popular story describing alert fatigue.