The quality or state of being alarming; the degree to which something causes worry, fear, or concern.
From alarming (adjective, causing alarm) plus the suffix -ness (creating a noun that expresses a quality or state), following standard English word formation.
The 'alarmingness' of a situation depends heavily on context—a car horn is alarming at 3 AM but barely noticed at noon, showing how our brains adjust alarm responses based on expectations.
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